Add and configure Specta and Expecta.

Next: Find a way to access repos from the test suite.
Add a PCH file for the tests.
Delete Git_Tests.m.
Add SSZipArchive as a submodule.
Add fixtures.zip as a bundled resource to the test target.
Add the nesscery classes to access the bundled git repos.
Remove `IDTGitModelSpec`

I’ve decided to break specs into multiple PRs.
Merge pull request #11 from PiersonBro/tests

Tests