Add an Unload voice for when a unit is unloading.
Merge pull request #3591 from ScottNZ/voices

Add an Unload voice for when a unit is unloading.
Add WAngle.ArcTan().
Add Gaussian sampling functions to WRange, WVec.
Convert ProjectileArgs to world coords.
Split TeslaRenderable out from TeslaZap.
Rewrite GravityBomb with world coords and gravity.
Rewrite bullets using world coords and improved trails.
Convert Missile to world coordinates. Fixes #3347. Closes #3434.
Use a properly sampled Gaussian for the tesla zap path.
Remove obsolete Gauss1D/Gauss2D functions.
Add WVec.ToCVec() extension method.
Remove PSubVec from AttackWander.
Remove obsolete PSubPos and PSubVec.
Remove obsolete functions from Traits.Util.
Use WAngle.ArcTan in Traits.Util.GetFacing.
Fix Traits.Util style issues.
Remove obsolete PPos functions from Target.