Use Promises/A+ test suite

The implementation doesn't pass all tests yet :(
Remove multiple resolutions error

The test suite seems to expect that nothing happens in this case.
Fix makeResolver function never rejecting
Implement Promises/A+ 2.2.7.2
Implement Promises/A+ 2.2.1

`promise.then(null).then(function() {})` must still call the function.
Merge branch 'promises' of https://github.com/lluchs/Ractive into lluchs-promises
all tests passing up to 2.3.1
Implement Promises/A+ 2.3.1
all tests passing except 4...
all tests in the Promises/A+ compliance suite pass! w00t!
refactor promise.js
renamed promise -> Promise, as it is a constructor
rebuilt