Flush out towards / figure 8 strategy unit tests
Motel#rand_vector - generate new vector if invalid
Location#direction_to - return correct dir from loc to target

Previously direction from target to loc was being returned
Location#rotation_to - normalize coord diff before calc rotation

Previous unnormalized calculation resulting in incorrect
rotations
Add a few helper methods to movement strategy mixins

  - LinearMovement#moving_towards?
  - LinearMovement#dir_changed?
  - Rotatable#rotating?
  - TracksCoordinates#moving_towards_target?
Tweaks to Towards ms, add helper methods + a few comments

Specs also updated
Add movement integration tests for towards strategy and mixins
Test acceleration in movement mixins integration spec
Add special tags for integration tests, do not run by default