Adding support for u-blox generation 7 NAV-PVT will allow current exa…

[JasonRJ]

…mples using NAV-PVT to be backwards compatable.

Protocol >= 15 (Gen 8 and beyond) has a message length of 92
Protocol = 14 (Gen 7) has a message length of 84
Protocol < 14 (Gen 6 and eariler) does not support NAV-PVT

Fields added in protocol 15 (headVeh, magDec, magAcc) are not being parsed in current version of the library.

[PaulZC]

Hi (@JasonRJ ),
Thank you for submitting this PR.
We made a decision a while ago that we are not going to try to incorporate support for series 6 and 7 in the main library. We cannot verify the code as we have no hardware to test it on. But we do include a stand-alone example for series6/7 and I've included your pull request there. The code changes are here:
f6a1fe0
I did not include the getProtocolVersionHigh as it doesn't really add much when checking NAV-PVT - the message will have already have been checksum-checked and so we can assume the length is valid.
The changes are still in the release-candidate branch for now, but I will (hopefully) be able to update the master branch in a day or two.
Thanks again,
Paul