Change nav_msg_update to use -1 as an invalid TOW_ms value.
Make dedicated GPS time type (week num / time of week pair) and update library to use it.
Add PRN and SNR to navigation message.
Add CMAKE_INSTALL_PREFIX to cache in toolchain file so that install uses the correct path.
Add CMAKE_C_FLAGS to cache in toolchain file so that correct flags are used on the first build.
Add valid field to almanac struct.
Change order of elements in gps_time_t so they will be packed without padding for alignment.
Pack gps_time_t structs.
No longer need week_num in gnss_solution.
Remove cruft related to troop correction from calc_navigation_measurement.

The calculation was slow and not being used anymore.
Correct small inconsistency in math in PVT solver.
Filter PVT solutions based on DOP, sanity and legality.
Remove and tidy some debugging messages.
Remove pos_ned from solution struct. Calculate vel_ned in calc_PVT.
Merge pull request #1 from mikepurvis/master

Minor fix for compiling coord_system.h as c++
Valid flag for gnss_solution.
Process subframe now returns error codes.
Merge branch 'master' of github.com:swift-nav/libswiftnav
Add ned2ecef and ned2ecef_d functions to coord_system.
Merging from upstream