Add user-settable noise parameters for dungeon density to each mapgen,
except V6 which hardcodes this noise parameter.
Move the calculation of number of dungeons generated in a mapchunk out
of dungeongen.cpp and into mapgen code, to allow mapgens to generate
any desired number of dungeons in a mapchunk, instead of being forced
to have number of dungeons determined by a density noise.
This is more flexible and allows mapgens to use dungeon generation to
create custom structures, such as occasional mega-dungeons.
Previously dungeons > decorations > ores.
Decorations depend on the node they are placed on, and ore types are
increasingly able to place large continuous volumes of nodes, such as
strata. Decorations are increasingly being used underground.
The new order avoids a node being changed by ore generation after a
decoration has been placed on it.
The new order also avoids ores appearing in the walls of a dungeon if
the wall nodes match the local stone node.
Make tunnels wider and use the noise parameters of most other mapgens.
All other underground features are already identical to all other
non-mgv6 mapgens, this final change modernises and improves the tunnels.
Previously the only way to disable biomes was to 'clear' the registered
biomes in a mod, but this method causes large amounts of unnecessary
processing:
1. Calculation of 4 2D noises.
2. Looping through all nodes of a mapchunk replacing nodes with identical
nodes.
The new flag disables those operations.
Previously, caverns confused tunnel generation causing biome top and filler
nodes to appear in caverns.
Split 'generateCaves()' into 2 functions to separate tunnel and large
randomwalk cave generation.
In each mapgen re-order cave generation to generate tunnels before caverns.
Add new biome fields 'node_dungeon', 'node_dungeon_alt', 'node_dungeon_stair'.
If 'node_dungeon' is not defined dungeons fall back to classic behaviour.
Remove messy and imprecise dungeon material code from 'generateBiomes()'.
Code deciding dungeon materials is now in 'generateDungeons()' and uses the
biome at mapchunk centre for more precision.
Remove hardcoded 'MG_STONE' types as long intended.
