Add a minimalist formatter (c/quickfix style output)

Created by: smortex

This formatter outputs failures in a similar fashion to the C compiler — file:line:message — allowing straightforward integration with text editors like vim and without adding extra dependencies to the project (relying on the quickfix-window from vim or simlar feature for other editors).

One can configure his editor with the following line (vim) and start jumping between failures using the regular editor keybindings, without having to visualy parse the output from rspec to find out the file and line number he want to reach:

autocmd FileType ruby set makeprg=bundle\ exec\ rspec\ --format\ c