Clarify Comments and Fix Typos (#651)

Fixes many typos, and errors in comments.

* Clarifies many comments
* Grammar correction in config.pl help text
* Removed comment about MBEDTLS_X509_EXT_NS_CERT_TYPE.
* Comment typo fix (Dont => Don't)
* Comment typo fix (assure => ensure)
* Comment typo fix (byes => bytes)
* Added citation for quoted standard
* Comment typo fix (one complement => 1's complement)

The is some debate about whether to prefer "one's complement",  "ones'
complement", or "1's complement".  The more recent RFCs related to TLS
(RFC 6347,  RFC 4347, etc) use " 1's complement", so I followed that
convention.

* Added missing ")" in comment
* Comment alignment
* Incorrect comment after #endif

library/net.c

@@ -228,7 +228,7 @@ int mbedtls_net_bind( mbedtls_net_context *ctx, const char *bind_ip, const char
             }
         }
 
-        /* I we ever get there, it's a success */
+        /* Bind was successful */
         ret = 0;
         break;
     }