Feature Request: Forking on a transaction in a block

[amanusk]

Motivation:
Transactions in the block modify the state. For some simulations and test it is interesting to work with a state after some transaction but before another in the same block

API suggestion:
In addition to specifying a URL and block-id to the forking request, optionally add a tx index in the block (or tx-hash). Devent will then "play" all txs up-to the specified tx, (not including)

If the index is out of range or tx-hash was not part of the block, an error is returned.