A Fresh Pot

* Make latest Mocha (v2.0.1, mochajs/mocha@b7edc81) available in
	Teaspoon.
* Revise `env_comments.rb` templates to reflect the updated Mocha and
	change the default version to 2.0.1.
* Add a version list to the README, correct the extant listing.
* Update `lib/teaspoon/configuration.rb` to include the new hotness.
* Nitpick: Mention, in the README, that users should install Istanbul
	themselves. I'm super-dense I'll grant you, but this took me
	forever and a day to figure out.