feat: add quoter updated event

* use istanbul hardfork

solidity/Makefile

@@ -1,5 +1,5 @@
-SOLC = /usr/local/bin/solc
-EVM_VERSION = byzantium
+SOLC = solc
+EVM_VERSION = istanbul
 
 all:
 	$(SOLC) --bin SwapPool.sol --evm-version $(EVM_VERSION)| awk 'NR>3' > SwapPool.bin

solidity/SwapPool.sol

@@ -60,6 +60,8 @@ contract SwapPool {
 		uint256 amountOut
 	);
 
+	event QuoterUpdated(address indexed newQuoter);
+
 	constructor(string memory _name, string memory _symbol, uint8 _decimals, address _tokenRegistry, address _tokenLimiter) {
 		name = _name;
 		symbol = _symbol;
@@ -105,6 +107,7 @@ contract SwapPool {
 		require(!isSealed(QUOTER_STATE), "ERR_SEAL");
 		require(msg.sender == owner, "ERR_AXX");
 		quoter = _quoter;
+		emit QuoterUpdated(_quoter);
 	}
 
 	// Implements EIP173
@@ -251,8 +254,10 @@ contract SwapPool {
 		bool r;
 		bytes memory v;
 
+		// This is a GE specific feature. However, it can be removed to allow anyone to push fees into a common feeAddress (profit-sharing)
 		require(msg.sender == owner, "ERR_OWNER");
 		require(feeAddress != address(0), "ERR_AXX");
+		require(_value <= fees[_outToken], "ERR_BALANCE");
 
 		(r, v) = _outToken.call(abi.encodeWithSignature('transfer(address,uint256)', feeAddress, _value));
 		require(r, "ERR_TOKEN");