Feature: "Focused" specs

[ezzatron]

I've been trying out Ginkgo, a describe/it style testing framework for Go. One of it's awesome features is "focused" specs, which allow a developer to isolate individual suites and/or specs, without needing to pass filters via the CLI.

They function in a similar manner to Peridot's "pending" specs. The idea being that when you use an f prefix instead of an x, all specs except the prefixed ones are skipped.

IMO, this would be an even more useful feature than #181. I find it much easier to put an f in front of an it() block than to worry about running the Peridot CLI with a specific path or filter pattern.

We could of course still include a CLI mechanism, and base it off of the concept of "focused" specs. Gingko does this via the CLI options --focus=REGEXP and/or --skip=REGEXP.