TypeScript type definitions

[kettanaito]

Introduces a basic typings in TypeScript.

Subjected to merge after a prior discussion.

[lemcii]

React.HTMLAttributes rather than React.InputHTMLAttributes<HTMLInputElement> might be a better choice, I thought about adding all variants but that'd require type assertion.

[kettanaito]

What do you think about modularizing type definitions, @Ell10t?

[lemcii]

No objections here, if it makes it more manageable it's probably not a bad idea.

[kettanaito]

@Ell10t I will try to break it down then.

Apart from that, the only crucial thing that is left is a type definition of that [valuePropName] in various callbacks. Within createField scope it should be possible to do via generics, but I am not sure how to handle it in Form callback methods.

[lemcii]

Alright, if I get time I'll have a look into the generics as well.