Ability to run tests

[mtdowling]

The luarocks CLI has a test command that installs test dependencies and runs tests. That's nice, but I'd like Cyan to be my one-stop-shop for build tooling. The luarocks CLI also does't understand Teal, so to write unit tests in Teal, you need a non-trivial amount of build glue to compile then test. That build glue usually means pulling in yet another tool like Make to orchestrate the steps. Ideally Cyan could have a test task that:

1. Installs test dependencies when necessary based on a dev rockspec (e.g., <name>-dev-1.rockspec)
2. Auto-detects busted tests, but somehow supports other configurable testing frameworks
3. Doesn't require the user to pre-compile Teal files into Lua (it should automatically handle this and put the files in a build directory)