Match section headings with quoted attributes and other fixes

Values should stop at a comment marker
Comments don't have to be at the start of a line

See: https://www.kernel.org/pub/software/scm/git/docs/git-config.html#EXAMPLES
Merge pull request #2 from lee-dohm/master

Match section headings with quoted attributes, values stop at comments, and comments don't need to be at the start of a line