A few one-line enhancements. Closes #11.

[jhominal]

There are three logical changes in this pull request:

• A .gitignore file was added, to ignore Gemfile.lock and coverage (same as grit_adapter);
• The :committer information is set, to the same information as :author - closes #11;
• The Index#get_parents method modified the parents argument - but, in the use that is made by Gollum::Committer, the parents array would be modified to contain an array of Rugged::Commit objects instead of Gollum::Git::Commit objects - that seemed weird and undesirable to me;

Now, these three should be separate issues, but I will confess that I did not feel like making two issue tickets for what, to me, feel like obvious improvements. If you feel that there is matter for a debate, feel free to tell me and I will open a separate issue, and amend this PR as necessary.

[dometto]

Now, these three should be separate issues, but I will confess that I did not feel like making two issue tickets for what,

No problem!

[dometto]

Many thanks again for scrutinizing gollum and the adapters. I worked on too much of this with too little time to get proper reviews, so it's great to get some now.

[bartkamphorst]

Excellent. Thanks @jhominal for all your work on this!