ANGLE_timer_query recast to ES EXT_disjoint_timer_query

A structured diff can be seen here: https://github.com/pyalot/WebGL/commit/c009d57a8d60a0c560c410b4d3d10e09df0006cb

Changes:

* Moved ANGLE_timer_query directory to EXT_disjoint_timer_query
* Replaced all instances of ANGLE_timer_query with EXT_disjoint_timer_query
* Replaced all instances of ANGLE with EXT
* Replaced the mirrors href with the khronos ES specification
* Updated the description from the khronos ES specification
* Renamed GLuint64Angle to GLuint64EXT
* Renamed WebGLTimerQueryAngle to WebGLTimerQueryEXT
* added the TIMESTAMP_ANGLE enum
* Fixed queryCounterEXT acceptable query param to TIMESTAMP_EXT as per ES specification
* Fixed getQueryParameterEXT to return boolean (not int) in case of QUERY_RESULT_AVAILABLE_EXT (the ES specification returns an int, but it's either 0 or larger than 0, indicating true or false)
* Deleted the "Additionally: ..." clause from getQueryParameterEXT because it is already contained in the ES spec
* Added a newtok definition for getParameter for the enums TIMESTAMP_EXT and GPU_DISJOINT_EXT
* updated the sample code to query availability and disjoint.