add API support for leveled nodes, used via these two functions:
`blockgame.register_leveled_node` registers leveled nodes for each level
up to a given maximum.
`blockgame.check_for_stacking` checks whether a given node is
supposed to stack with its vertical neighbors, and if so handles that.
`blockgame.register_node` now works both when the provided name includes
a mod name, and when it doesn't.
previously, including a mod name would break things, making the actual
name used for registration include the mod name twice.
leaves will now, upon beginning decomposition, check if there are
decomposing leaves on top of them which can fall down onto them. this
fixes an error where this situation would leave the top leaves visually
floating over the bottom leaves, even when there was space for them to
stack.
decomposition will no longer happen unless the decomposing leaves are
touching a dirty node. thus, they can now be used for decoration in
non-dirty locations.
decomposing leaves will now check if they can stack after being
constructed, fixing an error where there would be decomposing leaves
floating over other decomposing leaves.
leaves now call `minetest.check_for_falling` at their position when
decomposing into air. this fixes an error where falling nodes would be
left floating above decomposing leaves once said leaves disappeared.
saplings can now replace alive leaves when growing (and other nodes can
easily be added in the future).
previously, instead of saplings, it was accidentally the case that
alive leaves growth worked like this when growing out of sapling,
instead of actual sapling growth.
make growing leaves turn into alive leaves if they should do so.
previously, this didn't happen for leaves that exceeded their max
distance from supporting node.
saplings now only check for groups, not specific nodes, when determining
whether they are supported. the previously checked nodes are now in the
new group that's being checked.
make sure that the node at the placed position is actually a decomposing
leaves variant before doing anything else. (this may not be the case,
since a node may start falling immediately after being placed.)
make decomposing leaves no longer traverse nodes that don't affect their
decomposition rate, when determining said rate. this means that they're
only affected by nodes that either touch them directly, or touch nodes
that affect them.
leaves now have a higher chance of turning into dirt, the higher they're
piled within the node. full stacks (taking up an entire node) always
turn into dirt.
decomposing leaves now stack in layers, each one 1/4 of a node in
height.
currently this doesn't affect their behaviour, beyond making them stack
when placed or landing.
using the new falling node hooks provided by `bg_api`, add alternative
versions of existing stoneworking recipes, where instead of pummeling, a
stoney node must fall onto the input nodes with sufficient force.
note that since the only currently existing stoney node that can fall,
loose cobblestone, is unobtainable without cheats, so are these recipes.
