Support assertions with two arguments.

In another word, support equal, notEqual, strictEqual, notStrictEqual, deepEqual and notDeepEqual methods.
Add more tests for option prerequisites.
Seeking for better method names.
SourceInstrumentor should ensure option prerequisites just once.
Extract numberOfTargetArguments function out to eliminate duplication.
Merge pull request #2 from twada/twoargs

Support assertions with two arguments.