HE bug workaround; new models; balancing

-Partial workaround for HE bug; doesn't eliminate the problem, but helps
catch some cases.
-Added 20mm machinegun
-20mm AC weight decreased to 225 kg, round length increased
-20mm and 30mm HMG rounds/min halved; round length increased to
compensate.  20mm clip reduced from 120 to 75. Overall damage output is
similar.
-Fix for quiet 203 howitzer
-Fix for ACF sound tool not resetting 1.0L i4 special to proper pitch
-Updated descriptions for i5/v10
-Slightly reduced torque for 3.9L i5
-Reduced flywheel inertia for 1.0L i4 special
-Reduced flywheel inertia for 5.3L v10 special
-Added 2.4L v6 special
-Added 3.0L v12 special
-Added gamerpaddy's new single, vtwin, and standalone electric models
-Added Lazermaniac's new MG and HMG models
Updated models, AC20 fire rate

-Updated emotor standalone and single cylinder model bodygroups
-Fixed 7.62mm MG model size
-Fixed 20mm AC firing too fast
* New bullet features, DP update

-Added per-bullet callbacks OnPenetrated, OnRicochet, OnEndFlight, PreCalcFlight, PostCalcFlight.  -HandlesOwnIteration bullet key to disable bullet iteration.
-Battle DP mode can now optionally disable noclip.
* Version + bullet callback docs

-Forgot version num
-Added documentation for bullet callbacks in the readme
Added i3, fixed v10 phys

-Fixed v10 model physbox
-Added i3 engines
Merge remote-tracking branch 'upstream/master'

Conflicts:
	lua/effects/acf_muzzleflash/init.lua