v890 - FEATURE UPDATE: Weapon Progression

We've added a new weapon progression system to Squirrelmageddon! Still a few bugs left to fix, but the SquirrelTech is suitable for general usage at this stage!

- kills unlock levels.
- levels increase weapon proficiency
- proficiency increases accuracy and reduces spread, increases reload and re-chamber speed as well as increasing hit damage

[h2]Lots of other changes along the way including:[/h2]
- working turrets (character deploy-able soon!)
- weapon balancing
- laser rifle weapon added
- fixed: start button crash if no mission selected
- audio fix: weapon pickup
- more map lighting fixes

[h2]Planned features coming ASAP:[/h2]
- deploy-able plasma turrets (pack and move turrets)
- weapon specialization (immediately increase proficiency by 1 level - 1 time use per character)
- shops, training and suit upgrades
- more Steam Achievements
- more missions
- intel pickups that unlock missions
- characters can join a faction resulting in faction specific missions / objectives becoming available
- single player squirrel missions