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
diff --git a/scripts/config.pl b/scripts/config.pl
index 8921a87..2757f17 100755
--- a/scripts/config.pl
+++ b/scripts/config.pl
@@ -70,7 +70,7 @@
                               used:
                                 $config_file
     -o | --force            - If the symbol isn't present in the configuration
-                              file when setting it's value, a #define is
+                              file when setting its value, a #define is
                               appended to the end of the file.
 
 EOU