Add support for EIP-234 and EIP-1898

[GCdePaula]

EIP-234: Add blockHash to JSON-RPC filter options.
EIP-1898: Add blockHash to JSON-RPC methods which accept a default block parameter.

These two EIPs are closely related, and allow for querying the blockchain's state at a specified block hash. I've a draft implementation of these two ready and tested :)

There are two issues I'd like some guidance on, though.

The first is that, the way I was approaching it,EIP-1898 requires changing the signatures of a reasonable amount of methods of the trait etheres_providers::Middleware. Specifically, changing the types of Option<BlockNumber> to Option<BlockId>. Is this reasonable? I've also tried changing the type to something like Option<T> where T: Into<BlockId>. However, this has the downside that every time we pass a None, we have to type annotate the calls. Thoughts?

The second relates to testing. Ganache does not implement EIP-1898 (trufflesuite/ganache#745). It can be tested with geth, however, which is what I did.

How should I proceed? Should I open a PR?

Cheers!

[gakonst]

I personally find the None<()> annotation to be super ugly, so I'd more supportive of this first approach. This would be a breaking change (and that's fine since we're pre-1.0), and would be easily fixable by passing BlockNumber::Latest.into() (or similar) wherever the API is consumed

Testing the feature with geth SGTM!