Ethereum-rpc-client

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- Add `get_block_by_number` and `get_block_by_hash`

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- Default calls to `call()` and `send_transaction()` to be from the coinbase
address if no address is specified for the `from` address.

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- Fix hex encoding of `value` in transactino params.
- Pull `from` value from defaults when using the `call` method.

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- Add `get_transaction_by_hash` method.

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- Add `get_accounts` for `eth_accounts` endpoint
- Add `get_block_number` for `eth_blockNumber` endpoint

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- Initial release