0.3

- main: handle cases where the conn might be broken when sending (MR 3)
- stm_agps.py: don't fail if one of the AGPS files is missing (MR 2)
- stm_agps.py: don't error out if the gnss module doesn't return data (MR 2)
- systemd: Make service 'simple' instead of 'oneshot' (MR 1)
- stm_agps: readjust/shorten delay in readline()
- stm_agps_serial: don't reinitialize self._buf
- stm_agps: allow setting a custom device read command

0.2

- new 'driver' for STM serial devices (in contrast to the existing one
  for gnss devices)
- fix polling for data from devices