New models for cannon and short barrel cannon.

TY Lazermaniac
Engine buffs, Stubbyguns, updated cannon models

-Buffs to large B6, V8 and V12; small v12s and 13L v12 special  received
minor buff
-New multifuel v6 special
-Turbines now require fuel but have crazy output power
-Short barrel cannons added, these trade penetrative abilities and
accuracy for size and light weight
-37mm cannon added
-Fixed anims on lazermaniac's new cannon models
whoops

revision and changelog updated
Fixed something in cannon models
Note to self:

Make sure you check you don't get extra text on a ctrl-a ctrl-c.  Dammit
sexy undo!
Short-Barrel Cannon Adjustments

Gun weight decreased a bit to account for heavier shells. RoF changed
slightly.
Merge remote-tracking branch 'upstream/master'