Add declaration file to support TypeScript better

[chiro-hiro]

It's a little bit hard to use this package in TypeScript. I hope, this pull request could make this package is more friendly with TypeScript developers.

[levity]

Thank you! This looks good. The only question I have is, why do all the types start with I? Is this a TypeScript convention I'm not aware of?

[chiro-hiro]

I is stand for interface, some other projects are also use this kind of naming. For example, you type I then the IDE could suggest all interfaces.

I've found it's convenience then I put it here.

[chiro-hiro]

@levity Hi, Are we have any update here?

[levity]

Hi @chiro-hiro, thanks for the reminder, I'll merge this now

[levity]

Published 0.12.0 to npm with this change

[chiro-hiro]

@levity If there are anything need to be changed, just let me know. I will keep one eye on it and update interfaces.

Thanks,

[islishude]

@levity Hi,the type files are ignored on npm,I just filed a pr to fix this #33