Kesslergame

- Added `custom_sprite_path` property to `KesslerController` to automatically grab and load custom ship sprites from
the `graphics/images` directory

- Added mypyc compilation for performance increases. Credit to Jie Fan for the code + testing

- Fixed bug with only a single ship getting mine blast damage within the blast radius
- Fixed error in mine cooldown
- Added invincibility for mines during respawn

- Multiple changes to enhance/optimize calculations
- Reduction in calls to transcendental functions in math/numpy
- Reduced numpy calls for non-vector/less inefficient implementations
- Refined collision checks
- Changed destruct order to asteroids before ships
- Added `time_limit` to game state info passed to controller
- Fixed bug in mine detonation where coincidence with asteroids/ships caused undesired destruct behavior
- Changed such that if coincident with asteroid with 0 speed, momentum is imparted and split angles are uniform

- Changed `game_state` dictionary information to include an explicit `delta_time` entry representing the difference
in simulation time from one frame to the next as well as renaming `time_step` to a more accurate `sim_frame` which
represents the frame number that the sim is currently on.
- I.e. the default frequency is 30 Hz, and `delta_time` is constant so in this case has a value of 1/30.
- `sim_frame` will be 0 on the first frame of the sim and then increment to 1, 2,..., etc. until the sim reaches
termination criteria

- Added mine objects that can be placed by ships. Mines cannot move once placed, detonate after a fixed amount of
time, inflict a "hit" on any object within the blast radius (asteroids and ships), and impart momentum on
asteroids based on blast strength which is a function of the distance of the asteroid from the mine placement
point. The blast momentum imparted is a linearly decreasing amount with the maximum at the mine location and goes
to 0 at the edge of the blast radius.