Windows Phone 8,0 cocos2d-x 3.0  changes

This pull request contains all of the changes to the cocos2d-x 3.0 cross platform code needed to support Windows Phone 8 (WP8). The code for WP8 will be submitted in a separate pull request. Cocos2d-x 3.0 is now running very well on Windows Phone 8,0.

The following changes were made to the cross platform code:

1. Added CC_PLATFORM_WP8 and CC_PLATFORM_WINRT
2. Disabled ccconsole code for WP8 and WINRT until networking code is added.
3. Fixed a texture leak in FontAtlasCache. The texture was being overwritten when a new char was added to the texture. The previous texture was not being destroy. See comments added to code.
4. Disabled webp code for WP8 and WINRT. MSOpenTech is not able to contribute webp code.
5. Added .wav support to audio. WP8 does not support .mp3
6. Changed nullptr to NULL in all variable argument lists. WP8 compiler cannot terminate variable arg list with nullptr. 
7. Fixed use of compile reserved works GENERIC, ABSOLUTE and RELATIVE for WP8 compiler
8. surrounds all #pragma marks with CC_PLATFORM_IOS and MAC to avoid the breaking on builds on other platforms.
9. Added the purging of the FontAtlasCache in CCDirector.
10. Please note that some tests are leaking textures in the texture cache. For example, ActionsTest exits with 15 refcounts on grossini.png so it is not being released.

Thank you for reviewing our pull request.