Expose the descriptor's command queue to Lua code.

doc/Makefile.am: Remove queue.h.texi.
doc/mud.descriptor.texi: Describe new callback and instance variable.
doc/mudcore.texi: Remove queue.h.texi.
src/Makefile.am: Remove queue.[ch].
src/descriptor.c: Send commands to Lua code.
src/descriptor.h: Remove the old command queue.
src/lua_descriptor.c: Implement callbacks.
src/lua_descriptor.h: Implement callbacks.
src/queue.c: Remove.
src/queue.h: Remove.
Ignore more texinfo-generated files.

.gitignore: New patterns.