Update to V1.5 - The Rattler is no more

This update replaces the old Rattler with the Rusty Carbine, a hard-hitting projectile-based weapon. Think of it as the vanilla plasma rifle, but a bit faster, a bit stronger and slower on its recoil frame to compensate.

After that, John Agitator's OCD will get the best of him and he'll reload.

Other changes:

• Bolt-Thrower now has a grenade shot in the center of the spread. This will increase its usefulness at midrange or against single targets.
• Some slight code cleanup.
• Skullcracker's autofire is now a little bit faster.
• Dual MGs got a slight accuracy buff.

Happy  HEAVY MACHINEGUN-ing!