support for another object with a compatible API

[deeprnd]

Currently the library doesn't support the stated feature of "All parameters must be Uint8Array, Buffer or another object with a compatible API".

Specifically, if the library is used with the client-side JS, and the Buffer object, while supporting the compatible API, but doesn't extend Uint8Array - the assertions across the library fail.

This PR fixes that by extending the verification to the Buffer object, beyond the Uint8Array.

The PR doesn't impair nor adds complexity to the library and opens it to more general use cases