docs: document difference between testeth and retesteth

[yxliang01]

From how I see from these documentations, retesteth is meant to be a next-generation testeth. I have spotted main differences so far:

1. Support concurrent execution of tests
2. not coupled with any particular Ethereum protocol implementation
3. worse performance(when using aleth client and one worker only) due to the need to start a node and communication is done via IPC (compared to simply calling a function in C++)
4. Not all tests supported yet. (TransactionTests / VMTests / RLPTests / BlockchainTests filling)
5. EVM trace rpc methods not specified yet

I think it would be great if the core developers can complete this list and document it somewhere as this is going to be useful for new users to understand.

Thanks

[yxliang01]

CC: @winsvega

[winsvega]

https://github.com/ethereum/retesteth/wiki

The TCP socket is faster as you don't need to start the client. But if you have 100 cores the performance could outrun testeth theoretically. Especially if to refactor boost and run tests in parallel from each testsuite. Right now only tests from one folder are parallel. Meaning one heavy test will make other threads wait for the folder to finish

If you have any questions on above wiki please let me know so I clarify the instructions and keep it updated. Also a well formated docs are wellcome.

[winsvega]

testeth from aleth is not supported father. retesteth has all the same feautures, but depends on a client provider for evm computations.