Add typescript declarations

[elsmr]

• [x] dist folder now contains index.d.ts with type declarations for all exports

I left the build setup untouched, added tsc only to output the index.d.ts file

I tried it out in a project where I use react-zdog and it works well for me :smile:

Let me know what you think!

fixes #22

[AurelienDud]

Hello. Adding type declarations was a good job ... but are there any plans to make it public by releasing a new version of the library? Thank you