Convert HSV object to string

I noticed the API has 

`toHex()`, `toRgb()`, `toHsl()` and to `toHsv()`.

Furthermore:

`toHRgbString()` and `toHslString()`, but why no `toHsvString()` function?

I guess it has been forgotten to add it here?
https://github.com/omgovich/colord/tree/master/src/colorModels