GeoInterface v0.2.0

Update for julia0.5 (#8)

* update for julia0.5

* remove julia 0.4 testing from travis

* x/y/z -> x/y/zcoord

closes #9

* some more x/y/z to xcoord/ycoord/zcoord

and adding Travis testing for 0.6 since nightly is about to diverge