Added 'yogi perf'

This plugin introduces performance testing to Yogi.

Example commands:

    # simple, will just tell you the results of perf testing against your working tree
    $ yogi perf

    # the kitchen sink
    $ yogi perf --ref v3.10.0 --ref v3.11.0 --working false --loglevel debug --timeout 500 --tmp /some/tmp/dir

`perf` obeys the Yogi pattern of executing all tests in all components if executed from the root of the repo, or just against your local tests if in a component directory.

There is an additional commit to `package.json` which will be added to this PR at some point that will introduce a new module dependency for the actual tool that does the perf testing, but that will need to be released first.

Passes `npm test`.