Math standard library

[jakhog]

There are some things that would be nice to have included in the ThingML toolchain when it comes to standard functionality, that does not quite fit into the action language, but still has standard libraries in all our target platforms.

The first concrete example of this is maths functions, e.g. the square root, powers, trigonometric functions...

A maths library with some abstract PIM functions and concrete PSM implementations would be good to include with the compiler (like we have "datatypes.thingml" now).

Other examples like string -> int/float parsing would also be nice to have in the future...