Rename resolves and rejects assertions

[mantoni]

The resolves and rejects assertions diverge from the naming convention use by Sinon assertions. In Sinon, resolves and rejects are used to program a stub or a fake, e.g. sinon.fake.resolves(42). The Sinon assertions to verify promises are sinon.assert.resolved(...) and sinon.assert.rejected(...).

I would therefore like to propose changing the names as follows:

• resolves -> resolved
• rejects -> rejected
• toResolveWith -> toHaveBeenResolved
• toRejectWith -> toHaveBeenRejected

[mroderick]

@hexeberlin let's try to tackle this on Friday