Fixed Downloadables instances now being unloaded automatically.
Changed the way game specific weapons are added to PlayerEntity.
Fixed some issues with SendProp changes in players.weapons.  Made projectiles methods more dynamic.
Added docstrings and comments to players.weapons.projectiles.

Added <weapon>_indexes for projectiles to iterate over projectile indexes of that type.

Removed an unused import.
Fixed some issues with SendProp changes in players.weapons.  Made projectiles methods more dynamic.
Fixed creating projectile methods dynamically.
Merge branch 'weapons' of https://github.com/Source-Python-Dev-Team/Source.Python into weapons