Add typescript types

[corollari]

This PR adds typescript types to the public API. I tried to be the least invasive possible with the current code and setup (without sacrificing type checking) so I simply converted some files into typescript and made typescript emit the declaration files.

The only changes to the build process will be:

• When building the code, npm run build-ts will need to be run in order to generate currencies.js and wallet_address_validator.js
• These two .js files should be treated as simple build artifacts, all new code changes should be applied to the .ts files instead.

[corollari]

@GusGold thoughts?

[dartess]

Currently the typescript seems to have no problem with recursive types. Or is it not so? Perhaps it is worth updating the request?

[dartess]

@mdcuk34 Do you plan to update the request to make merge possible?

@GusGold How do you look at this request? #49 here you are not against typescript. Should @mdcuk34 update this request?

Personally, it seems to me that in this case it would be more correct to put the declaration file at the root, instead of changing the build process.