- Proper error reporting when encountering syntax errors in a
config file (file, line number, column).
- Rewritten `config_write`, now with 99% less goto-spaghetti
- Error state in `git_filebuf`: filebuf write functions no longer
need to be checked for error returns. If any of the writes performed
on a buffer fail, the last call to `git_filebuf_commit` or
`git_filebuf_hash` will fail accordingly and set the appropiate error
message. Baller!