* eth/gasprice: implement feeHistory API

* eth/gasprice: factored out resolveBlockRange

* eth/gasprice: add sanity check for missing block

* eth/gasprice: fetch actual gas used from receipts

* miner, eth/gasprice: add PendingBlockAndReceipts

* internal/ethapi: use hexutil.Big

* eth/gasprice: return error when requesting beyond head block

* eth/gasprice: fixed tests and return errors correctly

* eth/gasprice: rename receiver name

* eth/gasprice: return directly if blockCount == 0
Co-authored-by: rjl493456442 <garyrong0905@gmail.com>