Git::Repository requires git 1.5 or higher

Fixes #54
handle older versions of git better

Fixes #54
remove the site/ directory from the release

This directory is built by the example site.yml in the git repo, and is
only desirable for the git repo.

Fixes #53
bump Path::Tiny version to 0.054

We rely on a few features of 0.054:

1) FREEZE/THAW/TO_JSON - YAML serialization in t/command.t
2) basename( SUFFIX ) - Statocles::Theme

Fixes #55