Solidity contract that accepts unverified substrate headers (#65)

* solidity contract

* continue

* upd

* cargo update

* fixes

* ehtereum_headers -> headers

* extracted some common stuff

* ethereum_sync.rs -> sync.rs

* make sync generic

* continue extracting

* continue

* add eth-contract argument

* continue

* some fixes

* contract v2

* continue

* more fixes

* more fixes

* deal with duplicated params

* removed multiple call_rpc variants

* bail_on_error!()

* fn submit_ethereum_transaction

* more fixes

* cargo fmt --all

* fix

* bail_on_arg_error!()

* fix

* fix

* remove async_extra stuff

* substrate-bridge.json -> substrate-bridge-abi.json

* get rid of substrate transactions hashes

* get rid of ethereum transactions hashes

* extracted contract bytecode to separate file

* cargo fmt --all

* avoid duplicate import in contracts

* removed Default::default()

* swapped configurations for sub2eth && eth2sub

* fix compilation

* do not double gas limit when submitting Substrate headers

* cargo fmt --all

* solidity contract removed

* consts

* extracted solc compilation details to separate file

* removed (obsolete in future Vec<u8> justification)

* fixed cli option description

* fix typos

* fix grumble

* extracted constants

* log decoded header

* cargo fmt --all

* comment

bridges/relays/ethereum/res/substrate-bridge-metadata.txt

@@ -0,0 +1,5 @@
+Last Change Date: 2020-04-28
+Solc version: 0.6.6+commit.6c089d02
+Source hash (keccak256): 0xdc46aff04e37129265223e507d17f1407a70cb1ecea3230e1eaa77a17586724d
+Source gist: https://gist.github.com/svyatonik/876b388f9507a8de242cb2db9547c4f0
+Compiler flags used (command to produce the file): `docker run -i ethereum/solc:0.6.6 --optimize --bin - < substrate-bridge.sol`