[release] v0.15.0 (flutter-mapbox-gl#856)

[release] v0.14.0 (flutter-mapbox-gl#756)

[release] v0.13.0 (flutter-mapbox-gl#719)

[release] v0.12.0 (flutter-mapbox-gl#603)

[release] update pubspec for v0.11.0 (flutter-mapbox-gl#585)

[release] update pubspec for v0.10.0 (flutter-mapbox-gl#536)

update version numbers for v0.9.0 release

Update CONTRIBUTING.md (flutter-mapbox-gl#401)

Fix stale pull, issues & changelog urls in the contributing guide.

[release] release v0.7.0 of flutter plugin for mapbox maps