* ReadBlockByNumber and ReadChainConfig return error
* Let's make rawdb package to return error. But by small steps.
High-level methods need to move first:
ReadBlockByNumber
ReadChainConfig
ReadBlockByHash
ReadHeaderByHash
WriteChainConfig
WriteDatabaseVersion
WriteBlock
DeleteTd
WriteTd
ReadTd
* Moving a few files to be more consistent
* Collecting together custom code under tg_ namespace
* Small cleanups
* Updating test cases
* Uncomment eth_gasPrice but still unimplemented