a bit of an engine mod

to increase variety in car parts. The new 'bigness' property is the
only one that's currently transferrable between car parts & items.
Yeah, there certainly needed to be another 'size' attribute. this one's
variable though, and can mean different things depending on context.
(plating thickness, cc of engine displacement, wheel radius, kilowatts,
etc.)

not ready yet. i just wanted to put what i had out there.
L instead of CC in veh part display

Also taking out long word 'combustion' from part name.
same deal for item types as the prev. commit.

mostly cosmetic. Also updating the struct name
it_veh_part -> it_var_veh_part
Merge remote-tracking branch 'dda/master' into bigness
making compile.
a copy/rewrite of consume_item for veh parts

this is to preserve some item properties while ignoring
the weird cases of consume_item.
fixing a misconception that i had about

% operator vs. negative numbers
sort of preserving veh part health

through remove & install processes.
Merge remote-tracking branch 'dda/master' into bigness

Conflicts:
	mapitemsdef.cpp
part_info().power going through part_power

this makes engines with bigness actually have variable power.

also, bumping bicycles. because it's not fair that they have the
same wheels that cars have.
wheel variety. 5 types, variable diameters,

and implemented traction stuff.
Merge remote-tracking branch 'dda/master' into bigness
Merge remote-tracking branch 'dda/master' into bigness