Add bats test suite

Issue #6

Bats (Bash Automated Testing Suite) can be found at [GitHub](https://github.com/sstephenson/bats)
And be installed via homebrew `brew install bats`

Only adds tests for things that were very easy to test

PS: I use this in my .tmux.conf to run tests

    bind b \
      send-keys -t 1 "bats test" "C-m"