Draft: Add gcc warnings checker

[Letme]

This is a simple regex for the GCC warnings and errors. I catch the first line of the warning but discard the subsequent lines with explanation of the warning. Regex to catch that (but then doesn't work on simple warnings) is:

"(?:(?P<path1>(?:[/.]|[A-Za-z]).+?):(?P<line1>-?\d+):(?P<col1>-?\d+):\s*(?P<severity1>[Ww]arning|[Ee]rror)|<.+>:(?P<line2>-?\d+)(?::\s*(?P<severity2>[Ww]arning|[Ee]rror))?): (?P<description1>.+)\n(?P<description2>\s+\d+\s+\|\s+.*\n\s+\|\s+.*\n)\n?"g

Anyway, to get me started this should be decent enough. Let me know if you agree, then I delete (instead of comment out) the asserts for the reported warnings and add some more lines to documentation.

Contributes to #48