[uart] Fix stupid weak errors
[gps] Fix NMEA pointer error
update changelog
Merge pull request #978 from fvantienen/bebop

UART and GPS bugs
[tests] skeleton for testing math lib with libtap

using [libtap](https://github.com/zorgnax/libtap) to create a [TAP](http://testanything.org) (TestAnythingProtocol) producer.
You can also run the test (if already compiled) with prove:
```
prove --exec '' tests/math/test_pprz_math.run
```
[tests] add libpprzmath.so to LD_LIBRARY_PATH for running tests
[travis] run math tests
[omap] start basic spi driver

totally untested...