1.6.1

Changes:

• housekeeping: Release Sextant 1.6 @RLittlesII
• feature: Added Xamarin.iOS NavigationViewController (#50) @RLittlesII
• housekeeping: add opencollective.yml @glennawatson
• housekeeping: remove unneeded .github files @glennawatson
• housekeeping: Added .github folder (#42) @RLittlesII
• housekeeping: Added package description (#39) @RLittlesII