Provide an argument matcher function that takes an argument

[nhaarman]

Currently there is argThat and argForWhich which take extension functions T.() -> Boolean.
These are useful in situations like:

verify(mock).call(argForWhich<List> { size == 3 })

However, in some cases using an argument is more natural. Proposal to add an argWhere function that takes a function (T) -> Boolean:

verify(mock).call(argThat<String> { this == "test" })
  // vs
verify(mock).call(argWhere<String> { it == "test" })

This is somewhat related to #134.