Remove MALLOC macro

MALLOC macro was a convenient way to use malloc.
This step prepares the system for replacing malloc
with another memory manager.
Remove malloc from resourceusage_t

The implementation of resourceusage_t no more uses calls to malloc and free.
Implement x11window_t and support modules

The object x11window_t encapsulates a top level X11 window.

The x11display_t type describes the connection to a X11 display
server. An object of type x11screen_t serves as reference for
a screen (monitor) attached to an X11 display.

A new type called x11drawable_t is introduced to describes
the back buffer (double buffering) of am x11window_t which
is created with configuration option x11attribute_INIT_DOUBLEBUFFER.

The x11attibute_t type supports the different configuration options.

The type glxwindow_t encapsulates a top level X11 window which
supports drawing with OpenGL.

Drawing functions and text functions will come next.