Matcher for reading from channels

Often we are asserting on reading from a channel. It would be useful to have one that could read from channel and make further assertions on the result.

e.g.

```go
c := make(chan int, 100)
// ...
expect(c).To.Receive().And.Equal(90)
```

This example has more than just the `Receive` functionality. It also includes some chaining. If is distasteful, then maybe the following would be more palatable:

```go
c := make(chan int, 100)
// ...
expect(c).To.Receive(&i).Else.FailNow()
expect(i).To.Equal(90)
```