✨ Add support for SHA-3

Follow-up to #14.

Currently this library only supports Keccak, which although has a shared history with SHA-3, produces a different result.

The goal of this issue is to devise a plan to introduce SHA-3 into this library, in addition to the current Keccak implementation, in the least impactful manner.

The phased transition from Keccak to SHA-3 as the primary algorithm provided by this library is as follows:

1. Introduce an API wherein either a Keccak or SHA-3 hash can be produced. (TBD)
2. In a new minor release, the current API ,new SHA3.SHA3Hash(), should be marked as deprecated with a note to use the new API introduced in phase 1. For compatibility, new SHA3.SHA3Hash() should be aliased to initializing a new Keccak hash using the new API.
3. In a new major release, the current API, new SHA3.SHA3Hash(), should be removed, and the path of least resistance in this library, in keeping with the library’s name, should be to produce a SHA-3 hash rather than a Keccak hash.

In addition to the code-level changes related to each of the above phases, there should be ample notice and engagement with dependent projects, wherever possible, to help ensure a smooth transition.

[canterberry]

@steakknife @miguelmota

This is delivered in #44, which updates the API to the following:

• new SHA3.SHA3Hash(256) works exactly as it does today.
• new SHA3.Keccak(256) initializes a Keccak-256 hash with the same API as above.
• new SHA3.SHA3(256) initializes a SHA3-256 hash with the same API as above.

[macalinao]

I just spent an unfortunate amount of time debugging this. This should be called node-keccak.