Added stub extension function

[pbochenski]

with this method one can define mock for class

val someMock = mock<Object>()

and then define stubs in test

someMock.stub { on { something } doReturn somethingElse }

It is useful when some tests reuse mock object but with different stubbing

[nhaarman]

Nice idea! Could you perhaps add some regression tests, like https://github.com/nhaarman/mockito-kotlin/blob/master/mockito-kotlin/src/test/kotlin/test/MockitoTest.kt#L375 ?

[pbochenski]

please let me know if this is enough, or should I add all variants of stubbing to this.

[nhaarman]

Spot on, thanks!