We had some fun exploring the STD UDLs for potential collisions,
we have learnt our lesson and know how to proceed.
Now is high time to start behaving and obeying C++ rules.
Added dim_angle, Angle concept etc.
Not really for merging, but fun to play with.(The main problem is that it doesnt conform to SI)
See https://github.com/mpusz/units/issues/99
Could try adding degrees etc in same way as non-si units
