Use optparse-clj for nice CLI options processing

Allows GNU style options clumping:

        $ bin/frak -ec foo bar baz
        ^(ba[rz]|foo)$

And nice failure messages:

        $ bin/frak foo bar baz --evil
        Failed to parse `--evil`: Invalid option
Merge pull request #7 from guns/optparse-clj

Use optparse-clj for nice CLI options processing