Remove flag name conflicts with raco test

[florence]

Issue #18 shows we need to do this, and now.

[rpless]

We currently collide on -c (coverage) and -e. In raco test -c interprets the argument as a collection and -e treats any output to stderr as a test failure. I think we should change -c to -f (--format). But I'm not sure I want to change -e.

[florence]

How about -n/--no-output-for?

[rpless]

Done at 115acbd