Support working with custom blocks and transactions #7
Description
It can be useful for users to use our iterators with their own "entity" types (block, tx, txinput, txoutput).
The simple approach, using our entities and converting at each iteration, can be slow and inellegant.
Should somehow let the user "plug in" her own entity types, and make the iterators work with them.
Should document the minimal requirements the custom types should satisfy (e.g. must have a rawsize, block_hash, txid attributes).
Also add an example to the examples page.