Fix for Key.enabled issue #1190

- Added `enabled` getter; this resets the key (soft) and then disables they key
- Added `_enabled` property and updated internal usage
- Updated document for `reset`.
Comment fix

- Added `@private`
Merge pull request #1271 from pnstickne/wip-1190

Fix for Key.enabled issue #1190
Polygon.contains was toggling the return value on each valid hit (thanks @Singularetantum #1265 #1266)
Text.updateText was incorrectly increasing the size of the texture each time it was called (thanks @spayton #1261)
Phaser.Polygon has been refactored to address some Pixi v2 migration issues (thanks @pnstickne for the original implementation #1267)

Polygon.area is now only calculated when the Polygon points list is modified, rather than on every call.

Phaser.Polygon can now accept the points list in a variety of formats: Arrays of Points, numbers, objects with public x/y properties or any combination of, or as a parameter list (thanks @pnstickne for the original implementation #1267)

Polygon.contains now correctly calculates the result  (thanks @pnstickne @BurnedToast #1267)
Small refactor to pass jshint.