West-East and North-South corridors can now have hell deaths

*There are now 3 supported spawn point scenarios:
1) The original south spawn points scenario requiring plenty of south
space.
2) A south spawn point scenario which can occur in 1 tile width
north-south corridors.
3) A east spawn point scenario which can occur in 1 tile width west-east
corridors

* The grim reaper can now use the lava hole's west use tile.

*World:getHellDeathSpawnPoints() -> World:checkHellDeathSpawnPoints()

* World:checkHellDeathSpawnPoints() is now simpler with no duplicated
code.

+World:lavaHoleUseTileUsable()
Merge branch 'hell-deaths' of https://github.com/MarkL1961/CorsixTH into hell-deaths
Comment changed
Merge pull request #6 from JASheppard/hell-deaths

• There are now 3 supported spawn point scenarios:
 1) The original south spawn point scenario which requires lots of south space.
 2) A new south spawn point scenario which can occur in 1 tile wide north-south corridors.
 3) A east spawn point scenario which can occur in 1 tile wide west-east corridors.
 I will add north and west scenarios tomorrow.

• The grim reaper can now use the lava hole's west tile.

• World:getHellDeathSpawnPoints() has become: World:checkHellDeathSpawnPoints(patient, hole_x, hole_y, grim_x, grim_y)

• There's much less code in World:checkHellDeathSpawnPoints() than used to be in World:getHellDeathSpawnPoints()* because lots of duplicated code has been removed and replace with a call to function which checks the usability of lava hole use tiles.

• + World:lavaHoleUseTileUsable(hole_x, hole_y, start_x, start_y, use_tile_x, use_tile_y)

• The spawn points for hell deaths are now determined in the first phase of the hell death die action.