Minor fixes (#94)

- Updates RPC return types
- Removes custom query types in favour of default eth 
    - This is largely to allow for proper hexadecimal formatting (provided by `hexutil`), as the API is very specific about formatting.

x/evm/types/querier.go

@@ -1,61 +0,0 @@
-package types
-
-import (
-	"math/big"
-
-	"github.com/ethereum/go-ethereum/common/hexutil"
-)
-
-// QueryResProtocolVersion is response type for protocol version query
-type QueryResProtocolVersion struct {
-	Version string `json:"result"`
-}
-
-func (q QueryResProtocolVersion) String() string {
-	return q.Version
-}
-
-// QueryResBalance is response type for balance query
-type QueryResBalance struct {
-	Balance *hexutil.Big `json:"result"`
-}
-
-func (q QueryResBalance) String() string {
-	return q.Balance.String()
-}
-
-// QueryResBlockNumber is response type for block number query
-type QueryResBlockNumber struct {
-	Number *big.Int `json:"result"`
-}
-
-func (q QueryResBlockNumber) String() string {
-	return q.Number.String()
-}
-
-// QueryResStorage is response type for storage query
-type QueryResStorage struct {
-	Value []byte `json:"value"`
-}
-
-func (q QueryResStorage) String() string {
-	return string(q.Value)
-}
-
-// QueryResCode is response type for code query
-type QueryResCode struct {
-	Code []byte
-}
-
-func (q QueryResCode) String() string {
-	return string(q.Code)
-}
-
-// QueryResNonce is response type for Nonce query
-type QueryResNonce struct {
-	Nonce uint64 `json:"result"`
-}
-
-func (q QueryResNonce) String() string {
-	return string(q.Nonce)
-}