gx.h - public domain
Written by Mårten Hansson <hmrten@gmail.com> in 2015.

Simple library for writing small graphical demos.
  - Provides basic keyboard/mouse handling and a highres timer.
  - Assumes 32 bit BGRX pixel format (0xRRGGBB in little-endian).

-- Documentation

  #define GX_DEFINE    - define this in exactly one source file
  #define GX_STATIC    - (optional) make all functions static

  You must also define one of these
  #define GX_W32       - use W32 implementation
  #define GX_X11       - use X11 implementation

  gx_init(title, w, h) - initialize and open a window with dimension w*h
  gx_exit()            - cleanup.
  gx_poll()            - read an event, returns 0 when no more events.
  gx_paint(buf, w, h)  - draw buf consisting of w*h 32 bit pixels onto window,
                         will stretch to fit window size.
  gx_time()            - return time in seconds since gx_init().
  gx_delay(s)          - sleep for at least s seconds.