Improve macro hygiene

This commit improves hygiene and formatting of macro definitions
throughout the library. Specifically:
- It adds brackets around parameters to avoid unintended
  interpretation of arguments, e.g. due to operator precedence.
- It adds uses of the `do { ... } while( 0 )` idiom for macros that
  can be used as commands.

library/x509.c

@@ -67,8 +67,15 @@
 #include <time.h>
 #endif
 
-#define CHECK(code) if( ( ret = code ) != 0 ){ return( ret ); }
-#define CHECK_RANGE(min, max, val) if( val < min || val > max ){ return( ret ); }
+#define CHECK(code) if( ( ret = ( code ) ) != 0 ){ return( ret ); }
+#define CHECK_RANGE(min, max, val)                      \
+    do                                                  \
+    {                                                   \
+        if( ( val ) < ( min ) || ( val ) > ( max ) )    \
+        {                                               \
+            return( ret );                              \
+        }                                               \
+    } while( 0 )
 
 /*
  *  CertificateSerialNumber  ::=  INTEGER