Compatibility for embedded systems

[mkalte666]

Greetings,

I was searching for a lib that only needs c++11 (RTOS we are using forces me to that standard atm) and and i came across this one.

So far it looks good ; however on the embedded system i do not have access to streams, and i also am happy with float precision. That resulted in a few edits to units.h: mkalte666@55b53a4

This allows me to compile (in my case with -DUNIT_NO_STREAMS -DUNIT_BASETYPE=float)

I suggest to add this functionality to this lib.

I hope you have a nice day :D