[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
```

Proposal and starting point for attacking #954