They have moved from opengl.org to www.khronos.org

Only use the first paragraph in the doc which contains an overview,
the result of the more detailed doc generated non valid xml, and
all math expressions was rendered poorly. Remove for now.

This is both for error logger events and debug events. It can be done
because error log and debug log are both opened with encoding utf8 since
OTP-20.0

Functions where missing and where without alternatives, and
the functions are available in wxWidgets-3.0.*.

So either I missed it or they where removed for a while in
wxWidgets-2.9 branch, but that should not be used anywhere as
it was only a development branch.

Fix some configurations so that it works with new doxygen and
with complete install outside of /usr/include/wx...

* zandra/stdlib/optional-callbacks/OTP-13801:
  wx: make wx_object callbacks optional
  stdlib: Make gen_fsm callbacks optional
  stdlib: Make gen_event callbacks optional
  stdlib: Make gen_server callbacks optional

With a bad timing in wx:batch() the driver could get stuck
handling commands without ever checking for gui events.

Avoid that by exiting loop after the driver have done cond_wait a
couple of times.