Implement stateDiff tracer, compatible with OpenEthereum

[ziogaschr]

This PR adds stateDiff tracer that is compatible with OpenEthereum.

stateDiff State difference. Provides information detailing all altered portions of the Ethereum state made due to the execution of the transaction.

The stateDiff tracer can be used in the following Ad-hoc Tracing methods:

• trace_call
• trace_callMany
• trace_rawTransaction
• trace_replayBlockTransactions
• trace_replayTransaction

p.s.: The remaining unchecked Ad-hoc Tracing methods will be added in a new PR, and will have stateDiff tracer support out of the box.

Differences with OpenEthereum

1. SSTORE in some edge cases are being persisted in state but are being removed from stateDiff storage results. (Happens only on 2 transactions on Mordor testnet)
2. When error ErrInsufficientFundsForTransfer happens, OpenEthereum leaves the tracer run producing negative balances, though using safe math for overflows it returns 0 balance, on the other hand the to account receives the full amount. Core-geth removes only the gas cost from the sender and adds it to the coinbase balance.
3. Same as in 2, but on top of that, the sender account doesn't have to pay for the gas cost even. In this case, core-geth returns an empty JSON, as in reality this transaction will remain in the tx_pool and never be executed, neither change the state.
4. On OpenEthereum the block gasLimit is set to be U256::max(), which leads into problems on contracts using it for pseudo-randomness. On core-geth, we believe that the user utilising the trace_* wants to see what will happen in reality, though we leave the block untouched to its true values.
5. When an internal call fails with out of gas, and its state is not being persisted, we don't add it in stateDiff output, as it happens on OpenEthereum.

[ziogaschr]

@meowsbits where's the best place to add the Differences with OpenEthereum section from the above notes in our docs? Do you remember if we have a way to add them within the generated docs?

[ziogaschr]

@meowsbits I handled all your comments. Please have a look at them and re-review. Let me know if you find anything else as based on your comments we did some good hardening.

[meowsbits]

Awesome work.