E2S11: Use empty SLFs to get rid of a store_map_dimensions call
E2S11: Use Shaxthal hive terrains for Hekuba's keep
E2S11: Add cave ambience sound source
E2S11: Timing and sound effect fading/volume adjustments
E2S11: Visual effect adjustments to the ending sequence
Use different credits backgrounds for 1.10 and 1.12, and E1 through E3
Replace lua/direction.lua with a new set of functions from mattsc

The new code is taken from mattsc's AI-demos add-on. See
<https://github.com/mattsc/AI-demos/blob/master/lua/ai_helper.lua>.
Wire the new hex geometry functions into the [store_direction] WML action
Add [set_facing] WML action a.k.a. Unit-Facing-o-Matic-3000
E2S11: More debug helper events
Add simple wrapper macros for the [set_facing] WML action
Don't go back to C++ in [set_facing] if the unit facing is unchanged

If the unit facing remains unchanged, we don't really need to go through
the wesnoth.extract_unit/put_unit sequence.
E2S11: Use FACE* macros instead of the noisy [store_direction] business
E2S11: Enforce more unit facings during cutscene sequences