Introduce color consts: Silver, Purple & Orange
Color4: Refactor class to remove Color4.cpp

* The static const Color4u definitions are define preprocessors now, in
order to allow a headers-only library implementation of this class.

* Remove static keyword from operator overloads
* Add inline keyword to << operator overload
math/helpers: Refactor class to remove helpers.cpp

(Now a headers-only library implementation)
Point2: Introduce couple aliases; width & height

* Rename: point_delimimter const variable is now ALL CAPS
* Add inline keyword to << operator overload
math/helpers: Update round func to use C++ templates

* Add documentation for round function
* Update documentation for rand function
Transformable: Rename position & color methods

  - Instance Vars
* Transformable::coords -> position_
* Transformable::color -> color_

  - Methods
* Transformable::getPosition -> position
* Transformable::getColor -> color
* Transformable::setPosition -> set_position
* Transformable::setColor -> set_color
Sprite,SpriteBatch: Rename several methods & vars

  - Sprite
* sprite -> sprite_
* Introduce sprite method; returns nom::Texture of Sprite

* state -> state_
* getState -> state
* setState -> set_state

  - SpriteBatch
* sheet_id -> sheet_id_
* getSheetID -> frame
* setSheetID -> set_frame
AnimatedSprite, SpriteBatch: Bit more refactoring

* AnimatedSprite: setCurrentFrame -> set_frame
* SpriteBatch: Add virtual keyword to frame method (AnimatedSprite re-implements this method)
Fix Github Markdown parsing

* Not adding a space in between the striked out text (~~) was causing
trouble with rendering.
Remove ignoring of MSVCPP & BitTorrent Sync files

(We no longer use these)
Add some documentation notes for onMouseWheel