Make fields on frame pub

Refactor to 2018 edition

Fix tile flipping code

Version bump dependencies.

Update to latest

Add support for ObjectGroup properties

Rustfmt pass and slight macro stylistic changes

Keep track of layer indexing and parse more tile data

Expose `parse_with_path`.

replace flate2 with libflate for portability

fixes #47

Fixes #41

Add tile-flipping support

Not sure if the method is optimal, but here is some tile-flippin' goodness.

Parse animation

Update flate2 to the latest version

Parse imagelayer

Also add test for parsed image layers.
The test can be also used as an example off how one can get data from
the parsed map.