API / documentation consistency updates

- The `disabled` property of various input classes has been inverted to `enabled`.
  Direct/internal usage of `disabled` has been transformed to `!enabled`.
- A `disabled` get/set property has been added to wrap `enabled`, and marked as @deprecated
  This ensures current API compatibility.
Updated documentation per current Phaser tag usage
Click Trampolines - support to trampoline pointer events into 'click' events

- This is needed to support Fullscreen on IE11 because IE only trusts 'click' events for this operation; click trampolines as a general solution, although they are only required in some "special" cases.
Pointer - minor documentation update for click trampolines
Pointe - removed extra whitespace
Input - Minor Pointer refactor and documentation updates

- `pointerN` are aliases to backed `pointers[N-1]` array.
  This simplifies (and increases the efficiency of) looping through all the pointers when applicable; also eliminates pointer-existance checks
  Removes various hard-coded limits (added MAX_POINTERS); changed `maxPointers` default
- Removed some special-casing from cases where it did not matter
- Removed `=== false/true`, `==` usage for consistency, changed missing value check to `typeof`, etc.
- Updated documentation for specificty; added `@public\@protected`
- `@deprecated` currentPointers due to odd set pattern; `totalCurrentPointers` is more appropriate.
The Gamepad.addCallbacks context parameter was never actually remembered, causing the callbacks to run in the wrong context (thanks @englercj #1285)
Animation.setFrame used the wrong frames array if `useLocalFrameIndex` was `false` and a numeric frame ID was given (thanks @Skeptron #1284)
readme update
docs fix.
Merge pull request #1257 from pnstickne/wip-1191

Input "enabled/disabled" API and documentation consistency updates
All of the Input classes now use the more consistent `enabled` property instead of `disabled`. I.e. you can now check `if (input.mouse.enabled)` rather than `if (!input.mouse.disabled)`. The disabled property has been moved to a getter for backwards compatibility but is deprecated and will be removed in a future version (thanks @pnstickne #1257)
Merge pull request #1282 from pnstickne/wip-trampoline-click

Click Trampolines - support to trampoline pointer events into 'click' events
Pointer.addClickTrampoline now adds in support for click trampolines. These  raise pointer events into click events, which are required internally for a few edge cases like IE11 full screen mode support, but are also useful if you know you specifically need a DOM click event from a pointer (thanks @pnstickne #1282)
Fixed onClickTrampoline jsdocs.
Merge pull request #1283 from pnstickne/wip-pointer-mgmt

Input - Minor Pointer refactor and documentation updates
The Input class has been given a minor refactor to tidy things up. Specifically:
    * pointerN are aliases to backed pointers[N-1] array. This simplifies (and increases the efficiency of) looping through all the pointers when applicable; also eliminates pointer-existance checks Removes various hard-coded limits (added MAX_POINTERS); changed maxPointers default
    * Removed some special-casing from cases where it did not matter
    * Removed === false/true, == usage for consistency, changed missing value check to typeof, etc.
    * Updated documentation for specificty; added @public\@protected
    * @deprecated currentPointers due to odd set pattern; totalCurrentPointers is more appropriate.
(thanks @pnstickne #1283)