V0.0.5b19 - 2020-02-16

Merge pull request #190 from alcarney/color

- Add back the ability to pass in parameter values directly to definitions
- Add `lerp` function to do linear interpolation
- Add `clamp` function that can be used to limit values in an array
- Add `colorramp` function that can map an array of values into a color range
- Update tests and docs