message: update changelog to released state
diff: # Unreleased Features
  Please add a note of your changes below this heading if you make a Pull Request.
  +# Releases
  +## [0.4.8] - 2019-02-25
  ### Added
  * `dump_errors()` utility function in odrivetool to dump, decode and optionally clear errors.
  * `f` command to ascii protocol to get encoder position and velocity feedback.
  @@ -16,7 +18,6 @@ Please add a note of your changes below this heading if you make a Pull Request.
  ### Fixed
  * Added required 1.5 cycle phase shift between ADC and PWM, lack thereof caused unstable current controller at high eRPM.
  -# Releases
  ## [0.4.7] - 2018-11-28
  ### Added
  * Overspeed fault
  