Update for RSpec 3 beta 2

1. Support new matcher interface.

    Do you prefer `alias` or `alias_method`? I'm using `alias` because it's RDoc-friendly and those matchers are not likely to be subclassed, but I can change to `alias_method` if you want.

2. Explicitly enable both expectation syntaxes.

    Both fashions `something.should be_like_this` and `expect(something).to be_like_this` are used in tests so I enabled them. As in above, I can change it if you want to gradually force one or another and warnings seem helpful.