Add Hash impls for Point and Rect

[mdsteele]

Looks like commit b00e889 removed the existing Hash impls for Rect and Point (by accident, I assume), which broke some of my code that was using HashMap<Point, T> in many places. This PR adds Hash impls back for Rect and Point.

[mdsteele]

Hmm, odd. One out of the six travis-ci builds (osx stable) failed, but the failure doesn't seem related to this change:

---- test_events stdout ----
	thread 'test_events' panicked at 'assertion failed: `(left == right)`
  left: `User { timestamp: 0, window_id: 0, type_: 32770, code: 456, data1: 0x1234, data2: 0x5678 }`,
 right: `User { timestamp: 3, window_id: 0, type_: 32770, code: 456, data1: 0x1234, data2: 0x5678 }`', tests/events.rs:41:5
note: Run with `RUST_BACKTRACE=1` for a backtrace.

[Cobrand]

The test failing is obviously not related (although we'll have to look into it at some point), this PR looks good to me so I'm merging it!