This commit adds:
- New driver for SBPv2
--- Support Piksi Multi, Swift Navigation's multi-band multi-constellation GPS
--- Proper parsing of SBP flags
--- Instant response to Piksi status changes (no more timeouts)
--- Support for Piksi Multi as a Single-Point-Positioning GPS or only onboard GPS
--- Incorporates horizontal and vertical accuracy estimates, and vdop.
- Updates driver for SBPv0
--- Continue support for previous Piksi
- Dispatches correct driver based on SBP version.
Andrew Tridgell
Niels Joubert