Create .gitconfig

[Avamander]

This file instructs git to:

• blank-at-eol looks for spaces at the end of a line
• blank-at-eof notices blank lines at the end of a file
• space-before-tab looks for spaces before tabs at the beginning of a line
• fix outputs warnings for a few such errors, and applies the patch after fixing them (strip is a synonym --- the tool used to consider only trailing whitespace characters as errors, and the fix involved stripping them, but modern Gits do more)
• autocrlf = input converts CRLF to LF on commit but not the other way around