reorganize file structures; allow for module-specific types

reorganize file structures; allow for module-specific types

* figl/runtime.scm: Rename from (figl low-level support).

* doc/low-level-glx.texi:
* doc/low-level-glu.texi:
* doc/low-level-gl.texi: Regenerated.

* figl/gl/low-level.scm:
* figl/glu/low-level.scm:
* figl/glx/low-level.scm: Moved here, from figl/low-level/foo.scm.

* maint/update-low-level-bindings: Update script for new locations, and
  to use type modules.

* figl/glx/types.scm:
* figl/glu/types.scm:
* figl/gl/types.scm: New module-specific types.

* figl/low-level/types.scm: Removed in favor of module-specific types.

* Makefile.am: Update.