Convert all Buffer types to Uint8Arrays

[alex-miller-0]

Uint8Array types are native to the browser, which is the primary medium for this SDK. Furthermore, these types play nicely with React Native, which would make this SDK much easier to integrate into mobile apps. Long ago when we were building our own mobile wallet, we had a lot of issues with RN/Buffer and had to switch to using the buffer package, which is still un use today.

We should remove all uses of buffer (and its Buffers) and switch to using Uint8Arrays. This will, however, be a large undertaking.

Related to #427

[paulmillr]

Any backwards compatibility concerns? Or, converting everything and releasing a new version is the plan?

[alex-miller-0]

Yes this will affect the API so it will require a major version bump.