Add glob syntax support for -t option

Example:

    harvey -t "spec/**/*.js"

Leaving this undocumented for now. The `-a` option still works, but it's less useful. In the future, it would be nice to specify a list of test files (with glob syntax support), perhaps as the last argument:

    harvey [options] FILE...
    harvey -c config/dev.json "test/foo/**/*.js" "test/bar/**/*.js"