Allow runner to hold the git_info object so plugins can make use of it

Inspired by this PR to add some extra params to the uploldz plugin, i've made the `git_info` object available in the LolCommits::Runner class itself, so plugins can grab any info they like from it.

Also did some other small code clean ups in Runner and GitInfo classes.

I'll close #224 now in favour of this PR instead.  Thanks for you're contribution @clops!