function issueTokens(address _beneficiary, uint256 _amount) public onlyOwner {
        require(_beneficiary != 0x0 && _amount > 0 && tokensSold.add(_amount) <= tokensForSale); 
        ETCL.mint(_beneficiary, _amount);
        tokensSold = tokensSold.add(_amount);
        TokensPurchased(_beneficiary, _amount);
    }