Standardize header names and file locations

This is both a really big and a really small commit. It is small in
that it only contains renaming, moving and modification of include
directives caused by this.

It is really big in the obvious way of touching something like 200
files.

The new rules for naming files is simple: headers use the `.hpp`
extension. The rules for physical file layout is still kinda in
progress, but the basics are also simple:
 * Significant parts of functionality get their own subfolder
   * Benchmarking is in `catch2/benchmark`
   * Matchers are in `catch2/matchers`
   * Generators are in `catch2/generators`
   * Reporters are in `catch2/reporters`
   * Baseline testing facilities are in `catch2/`
 * Various top level folders also contain `internal` subfolder,
   with files that users probably do not want to include directly,
   at least not until they have to write something like their own
   reporter.
    * The exact files in these subfolders is likely to change later
      on

Note that while some includes were cleaned up in this commit, it
is only the low hanging fruit and further cleanup using automatic
tooling will happen later.

Also note that various include guards, copyright notices and file
headers will also be standardized later, rather than in this commit.

src/catch2/internal/catch_test_case_registry_impl.cpp

@@ -0,0 +1,120 @@
+/*
+ *  Created by Martin on 25/07/2017
+ *
+ *  Distributed under the Boost Software License, Version 1.0. (See accompanying
+ *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+#include <catch2/internal/catch_test_case_registry_impl.hpp>
+
+#include <catch2/internal/catch_context.hpp>
+#include <catch2/internal/catch_enforce.hpp>
+#include <catch2/interfaces/catch_interfaces_registry_hub.hpp>
+#include <catch2/internal/catch_random_number_generator.hpp>
+#include <catch2/internal/catch_run_context.hpp>
+#include <catch2/internal/catch_string_manip.hpp>
+#include <catch2/catch_test_case_info.hpp>
+#include <catch2/catch_test_spec.hpp>
+
+#include <sstream>
+
+namespace Catch {
+
+    std::vector<TestCaseHandle> sortTests( IConfig const& config, std::vector<TestCaseHandle> const& unsortedTestCases ) {
+
+        std::vector<TestCaseHandle> sorted = unsortedTestCases;
+
+        switch( config.runOrder() ) {
+            case RunTests::InLexicographicalOrder:
+                std::sort( sorted.begin(), sorted.end() );
+                break;
+            case RunTests::InRandomOrder:
+                seedRng( config );
+                std::shuffle( sorted.begin(), sorted.end(), rng() );
+                break;
+            case RunTests::InDeclarationOrder:
+                // already in declaration order
+                break;
+        }
+        return sorted;
+    }
+
+    bool isThrowSafe( TestCaseHandle const& testCase, IConfig const& config ) {
+        return !testCase.getTestCaseInfo().throws() || config.allowThrows();
+    }
+
+    bool matchTest( TestCaseHandle const& testCase, TestSpec const& testSpec, IConfig const& config ) {
+        return testSpec.matches( testCase.getTestCaseInfo() ) && isThrowSafe( testCase, config );
+    }
+
+    void enforceNoDuplicateTestCases( std::vector<TestCaseHandle> const& functions ) {
+        std::set<TestCaseHandle> seenFunctions;
+        for( auto const& function : functions ) {
+            auto prev = seenFunctions.insert( function );
+            CATCH_ENFORCE( prev.second,
+                    "error: TEST_CASE( \"" << function.getTestCaseInfo().name << "\" ) already defined.\n"
+                    << "\tFirst seen at " << prev.first->getTestCaseInfo().lineInfo << "\n"
+                    << "\tRedefined at " << function.getTestCaseInfo().lineInfo );
+        }
+    }
+
+    std::vector<TestCaseHandle> filterTests( std::vector<TestCaseHandle> const& testCases, TestSpec const& testSpec, IConfig const& config ) {
+        std::vector<TestCaseHandle> filtered;
+        filtered.reserve( testCases.size() );
+        for (auto const& testCase : testCases) {
+            if ((!testSpec.hasFilters() && !testCase.getTestCaseInfo().isHidden()) ||
+                (testSpec.hasFilters() && matchTest(testCase, testSpec, config))) {
+                filtered.push_back(testCase);
+            }
+        }
+        return filtered;
+    }
+    std::vector<TestCaseHandle> const& getAllTestCasesSorted( IConfig const& config ) {
+        return getRegistryHub().getTestCaseRegistry().getAllTestsSorted( config );
+    }
+
+    void TestRegistry::registerTest(std::unique_ptr<TestCaseInfo> testInfo, std::unique_ptr<ITestInvoker> testInvoker) {
+        m_handles.emplace_back(testInfo.get(), testInvoker.get());
+        m_infos.push_back(std::move(testInfo));
+        m_invokers.push_back(std::move(testInvoker));
+    }
+
+    std::vector<std::unique_ptr<TestCaseInfo>> const& TestRegistry::getAllInfos() const {
+        return m_infos;
+    }
+
+    std::vector<TestCaseHandle> const& TestRegistry::getAllTests() const {
+        return m_handles;
+    }
+    std::vector<TestCaseHandle> const& TestRegistry::getAllTestsSorted( IConfig const& config ) const {
+        if( m_sortedFunctions.empty() )
+            enforceNoDuplicateTestCases( m_handles );
+
+        if(  m_currentSortOrder != config.runOrder() || m_sortedFunctions.empty() ) {
+            m_sortedFunctions = sortTests( config, m_handles );
+            m_currentSortOrder = config.runOrder();
+        }
+        return m_sortedFunctions;
+    }
+
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    void TestInvokerAsFunction::invoke() const {
+        m_testAsFunction();
+    }
+
+    std::string extractClassName( StringRef const& classOrQualifiedMethodName ) {
+        std::string className(classOrQualifiedMethodName);
+        if( startsWith( className, '&' ) )
+        {
+            std::size_t lastColons = className.rfind( "::" );
+            std::size_t penultimateColons = className.rfind( "::", lastColons-1 );
+            if( penultimateColons == std::string::npos )
+                penultimateColons = 1;
+            className = className.substr( penultimateColons, lastColons-penultimateColons );
+        }
+        return className;
+    }
+
+} // end namespace Catch