CLI should include subdirectories

[vlucas]

Currently, there is no way for me to run tests in subdirectories, or to even specify a directory to run tests in. I was expecting to be able to do something like mocha-casperjs tests/mysubdirectory, but it errors with CasperError: Can't find module [blah blah blah].

Running tests with the mocha-casperjs command by itself just outputs 0 passing (0ms). This doesn't allow me to organize my test suite at all, and is contrary to the behavior I would expect.

I recommend allowing a parameter that would be EITHER a single file to run, OR a directory of files to run.