Fixed libX11, libXrender bindings for macos and linux.
Added pkg-config support to xlib, xrender, cairo, cairoxlib
Some fixes to xlib wrapper
Fixed XClientMessageEvent struct, added equals operator fot TAtom from unsigned, added xclient union field access proc to XEvent
Added use_pkg_config, use_pkg_config_static conditionals to xlib, cairo
Fixed xrender.nim for use_pkg_config
Moved complex pragmas for xlib and cairo into separate included files. Fixed xkb bindings.
Merge pull request #523 from exhu/x11fix

X11, cairo bindings fixes