Add support for TypeScript

[baileyherbert]

This pull request:

• Adds a default export so TypeScript users can import it with import and not require. This is important because packages imported via require() do not have intellisense in TS.

• Adds a type definition file which will enable intellisense in supported editors (Visual Studio Code, Atom, and WebStorm to name a few). The function signature shows in both JavaScript and TypeScript projects, but the full intellisense of course works best in real TypeScript projects.

Function signature:

Intellisense:

Each item is fully documented:

Full error checking:

[yuanchuan]

Thank you @baileyherbert !

I'm not a TypeScript user. Could anyone please help with reviewing these changes?

[baileyherbert]

No problem, @yuanchuan. In the mean time I have updated the PR with better screenshots and a more thorough explanation. Cheers!

[yuanchuan]

Merged, thanks!