Add typescript definitions

[jstarry]

Problem

There are no type definitions available for TypeScript users

[jstarry]

@pabigot I'd like to tackle this by migrating the project to use TypeScript and auto-generate the type definitions. Is this a change you would accept?

[pabigot]

I don't know; I did play with TypeScript a while back, but not enough to use it. Depends on how much of a maintenance impact it has.

[bmeeder22]

+1 would like this as well

[dfl-zeke]

+1 it's must have for this kind of lib.

[jstarry]

@bmeeder22 @dfl-zeke just a heads up that Solana maintains a separate fork and npm package @solana/buffer-layout that you can use for TypeScript types until those changes are upstreamed into this repo. You can find it here: https://github.com/solana-labs/buffer-layout