Rename CoroutineMock to CoroutineFunctionMock

[Martiusweb]

The name CoroutineMock is confusing (see #100, #101, etc) as it's the mock of a coroutine function, not a coroutine itself.

CoroutineMock should be renamed to CoroutineFunctionMock. CoroutineMock will be marked as deprecated and removed in 1.0.