remove backup files from vim and modify gitignore
Merge branch 'servo_control' of github.com:psas/stm32 into servo_control
PWM changes for servo_control firmware.

PWM now is standardized on 'ticks'.
New function pwm_us_to_ticks will convert from microsecs
  to ticks.

Added new thread for testing pwm. This thread can be deleted
later.