decompress tiles using gzip-hpp

[mapsam]

Let's allow users to pass in gzipped tiles, and auto-detect if they are gzipped.

cc @GretaCB @springmeyer

[springmeyer]

👍 plan move on this once https://github.com/mapbox/gzip-hpp/milestone/1 is finished.

[springmeyer]

underway at #73 #95

[springmeyer]

done in #95