raylib v2.6.0

This release is just intended to keep a tag of raylib 2.6 state before moving to the upcoming raylib 3.0 release.

On raylib 3.0 all modules globals have been moved to a global context state, using the name of the module (in capitals) as the object instance. It implied a very big refactoring of all the code, renaming ALL the global variables used in every module... but new code is more readable and global variables around the code are easily detected.

raylib 3.0 develop branch was used on GGJ2020 to develop a game and compile it for Desktop and HTML5 platforms, it worked very good. raylib 3.0 has also been tested on RaspberryPi and compiled with no errors for all CI available platforms. At this point raylib 3.0 should be stable.

From now on master branch will include this new design, a 2.6 branch will be kept for reference.