Added a routine to handle textual includes in shaders.
Added a routine to handle textual includes in shaders.

This is currently unused (to be turned on in the next commit), but will be used by using #pragma include <name>.

Signed-off-by: Alastair Lynn <4665d361aaf271b139147017031ea99df777ca5a@gmail.com>

adam000/Apollo,adam000/Apollo,adam000/Apollo