Added combine and tests. Moved is_readable to helpers
Merge branch 'master' into combine

Conflicts:
	lib/understream.coffee
combine: added tests for objectMode true and false
Merge branch 'master' into combine

Conflicts:
	lib/understream.coffee
lint
combine: mix in
bail on test failure
combine: accept streams as array
combine: add tests for >2 streams
combine: moar tests
combine: update comment
unlint
test: combine: unnecessary var
Merge pull request #38 from Clever/combine

Combine