Trying to extract power-assert-formatter out.

empower module does not provide default formatter from now on.
power-assert module will compose assert object/function and formatter using empower function.
Bump to 0.3.0-dev
Testing assertions with two arguments again.
Move coffee-script-redux feature test to formatter.
Now assumes formatter is a function that takes context and returns formatted string.
Remove private clone of Function#bind for old browsers (please use es5-shim).
More tests.
Merge pull request #3 from twada/extract_formatter

Extract formatter