doc: Update compilation & installation docs.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
demos: c_simple: Fix segfault when x11 not compiled in

* This fixes segfault when we are not able to initialize X11 backend.

* Also changes GP_BackendExit() to be no-op for NULL pointer.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
backends,input: Move Input drivers to backends.

* These require linking against corresponding libraries
  and belong to the backends anyway.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
build: Fix linker ordering and build.

* Loaders are now in separate so library

* Linker flags order is fixed and missing
  flags are added.

This should fix build on Ubuntu.

DON'T FORGET TO RUN ./cofigure BEFORE make

Signed-off-by: Cyril Hrubis <metan@ucw.cz>