Add some metrics!

[aslilac]

Lots of other tools in the area have things like "whitespace lines" "comment lines" "code lines"

It could also be interesting to track "config lines" "testing lines" etc.

Downside would be that this all adds a lot of complexity and compute, and right now kc is very simple and fast. I'd probably make it be an opt-in flag at the very least to keep perf good on the default path.