Menu improvements, gameplay instructions, and assorted gameplay tweaks. — To The Death Steam update #1376721

HOW TO PLAY instructions added to main menu. Significant A.I. improvements made to Troop 4 bot. Is now a lot more aggressive. Bot spawners, pushable cannons and hoverboards now generate sparks to indicate when their health is low. A handful of improvements to layout randomization in several arenas. Some layout randomization added to the first two rooms of Bot Arena 6. Flamethrower tweaks. Rate of fire reduced, as the weapons was a bit overpowered. Also lessened the particle effects of fire as it was affecting frame rate in multiplayer. Elevator speeds fixed in Arena 9 (previously way too fast). Bot spawners will spawn replacements for killed bots more quickly. Players in both game modes now start all matches armed with grenades and a pistol, instead of empty handed. More updates coming very soon!