Updated rugged dependency to avoid flaky 0.21.0

0.19.0 compiles on OS X while 0.21.0 does not.
Merge pull request #32 from dankohn/patch-1

Updated rugged dependency to avoid flaky 0.21.0
Bump version to 0.2.6
Remove 'grit' from gemspec and add 'rugged'
Move Rugged::Patch out of Diff namespace
Remove patches that are not needed with rugged '0.2.1'
Passing parents.first is no longer necessary for diff
Add 'pry' as development dependency
Use Rugged::Blame to find the commit line

Requires a couple of hacks due to regressions in rugged 0.21.0
Bump octokit from 2.7.0 to 3.2.0
Upgrade rspec to 3.0.0
To find commit location, use orig_ instead of final_start_line_number
Use additional tracking options for more accurate blaming
Get rid of Rugged monkey patches, move them to Pronto::Git namespace
Extract Git::Patches, Git::Repository and Git::Remote
Move #blame to Patch from Line
Some specs for Git::Line
Use Forwardable in Git::Line
Some specs for Git::Patch
Use Forwardable in Git::Patch