Unify :output & :reporter

[NoahTheDuke]

Closes #7

->config now handles converting :output (external) to :reporter (internal). :output must be a symbol or sequence of symbols, and :reporter is a function. Logic for changing simple symbols to lazytest.reporters namespaced symbols now happens in ->config as well, so that all of the configuration-related logic is happening there instead of spread across the namespaces (cli, main, etc).

[seancorfield]

Once this is merged, I'll make a pass over my test runners and remove the :reporter references. Since the defaulting and qualifying is happening further down the call stack, I suspect I can simplify my code quite a bit! Thank you.