implementation of evm->native bridge

[taokayan]

Resolves #61 & #63 & #64

deployment prerequisites:

1- have evm runtime contract (eosio.evm), this contract (eosio.erc2o) deployed
2- an existing ERC-20 token on EVM side, for example, token deployed in 0x4d9dbb271ee2962f8becd3b27e3ebcd384ad3171

3- an existing mirrored token on native side, for example: goldgoldgold, if not, create & issue the mirrored token:

./cleos set code goldgoldgold eosio.token.wasm
./cleos set abi goldgoldgold eosio.token.abi
./cleos push action goldgoldgold create '{"issuer":"goldgoldgold", "maximum_supply":"1000000.0000 GOLD", "can_freeze":0, "can_recall":0, "can_whitelist":0}' -p goldgoldgold@active
./cleos push action goldgoldgold issue '{"to":"goldgoldgold", "quantity":"1000000.0000 GOLD", "memo":"issue GOLD"}' -p goldgoldgold@active

4- transfer a maximum mirrored supply to eosio.erc2o

./cleos transfer goldgoldgold eosio.erc2o "1000000.0000 GOLD" "eosio.erc2o" -c goldgoldgold -p goldgoldgold

5- deploy the implementation contract (this is done only once for all tokens)

./cleos push action eosio.erc2o upgdevm2nat '[]' -p eosio.erc2o

6- regsiter trustless bridge for the ERC-20 token:

./cleos push action eosio.erc2o regevm2nat '["0x4d9dbb271ee2962f8becd3b27e3ebcd384ad3171","goldgoldgold","0.1000 GOLD","0.0100 EOS",18,""]' -p eosio.erc2o

after that the token bridge is regsitered:

./cleos get table eosio.erc2o eosio.erc2o tokens
{
  "rows": [{
      "id": 2,
      "token_contract": "goldgoldgold",
      "address": "efb6a2241f3cc0e740a9aab830ef729130667574",
      "ingress_fee": "0.1000 GOLD",
      "balance": "0.0000 GOLD",
      "fee_balance": "0.0000 GOLD",
      "erc20_precision": 18,
      "_is_evm_to_native": 1
    }
  ],
  "more": false,
  "next_key": ""
}

7 - to transfer from EVM to native, a user needs to:

• 7a) call 0x4d9dbb271ee2962f8becd3b27e3ebcd384ad3171's approve(efb6a2241f3cc0e740a9aab830ef729130667574, amount)
• 7b) call efb6a2241f3cc0e740a9aab830ef729130667574's bridgeTransfer(to, amount, memo), where the "to" is the reserved address that maps to the native account

8 - to transfer from native back to EVM (memo = EVM token receiver address)
./cleos transfer nativeuser1 eosio.erc2o "1.0000 GOLD" "0xaAE508DCac0E36091127cEdaD989649bA601947b" -c goldgoldgold