[Hacktoberfest] Convert to typescript

[jsdario]

This task should not be very difficult since it's a single file library. I think we could gain significant value from it, achieving a lot of soundness in a pure functional library, with further mantainability for years to come.

[barthap]

Maybe converting to TypeScript is not necessary, but adding type declarations would be enough.
I made a PR #27 with colorsys.d.ts - my fork works pretty well with my TypeScript projects.

[jsdario]

Thanks for that

[jnguyenmt]

Did the version with the typescript file get published? I'm currently not seeing it in v1.0.22

[barthap]

Yeah, it is just on github master, but npm package doesn't seem to be updated.

Temporarily, you can install it directly from github: yarn add https://github.com/netbeast/colorsys.git or npm i --save https://github.com/netbeast/colorsys.git