Fixes Fatal error: Call to a member on a non-object

Fixes "Fatal error: Call to a member function addLine() on a non-object" when commit has 0 updated files
Add phpunit to require-dev section of composer.json
Handle detached HEAD state more correctly.

Repository::getBranches() no longer includes '(nobranch)' in this case.

Repository::getHead() now accepts an optional default branch, which
it will return if HEAD is detached *and* the default exists. Otherwise,
it returns the first existing branch.
Merge pull request #17 from NateEag/fix-get-branches

Fix fetching repo's branches when in detached HEAD state
Merge pull request #16 from MSylvia/master

Fixes fatal error when a commit has 0 updated files
Updating dependencies
Get commit body, fixes #1
Check for git version before using -c option, fixes #9
Branch fixes
Merged multidir branch with master