Examples for two ways to create Commits

This may help people wanting to do higher-level commit-ish things.
Merge pull request #157 from rick/bettar-examples-for-commit-creation

Examples for two ways to create Commits
Export the timezone for commits
Bump libgit2
Merge pull request #158 from libgit2/timezone-offsets

Export the timezone for commits
Bump libgit2
Bump libgit2
Index API has changed
Update libgit2 to d77f80d
Add ruby bindings for git_libgit2_opts()
fix doc string
Rugged::set_option() -> Rugged::Settings[]=
Fix Rugged::Settings on 1.8.7
Add getters to them options
Bump libgit2 to @5425097
Fix some tiny typos.

`Expeting` -> `Expecting`
Merge pull request #160 from arthurschreiber/patch-1

Fix some tiny typos.
Look for time_offset in rugged_signature_get

* Fall back on Time#utc_offset if time_offset is nil
Merge pull request #162 from jakeboxer/signature-get-time-offset

Look for time_offset in rugged_signature_get
bump libgit2 to fb60d2