Add test to penetrate to_deg to_rad conversions

Rounding errors from one to the other results in some corner cases where
precision is lost.
Use global CXXFLAGS to incorporate test submodule

Using new flags for sanitizer etc requires all libraries et al to be compiled
the same way. I.e. the same compiler flags should be used for both the library
as well as the tests.
Change coefficient order for degree converter
Update and add tests, plus fix incorrect test value
Rework deg, sec and min methods for vposition

Precision problems with conversion back and forth between degrees and radians
caused incorrect output for min and sec values, for example 30m00s became
29m60s. Same value but not correctly displayed. Lowering the precision from
double to float when computing number of minutes solved the problem. Computing
the seconds relies on the min-methods and the "precision loss technique"
therefore propagates.

Still not completely solved, i.e. the problem behind this and what better
technique to use is still unknown.