contract ERC20 is ERC20Basic {

  //Get EXH token amount that spender can spend from provided owner's account 
  function allowance(address owner, address spender) public constant returns (uint);

  //Transfer initiated by spender 
  function transferFrom(address _from, address _to, uint _value) public returns(bool ok);

  //Add spender to authrize for spending specified amount of EXH Token
  function approve(address _spender, uint _value) public returns(bool ok);

  //Emit event for any approval provided to spender
  event Approval(address indexed owner, address indexed spender, uint value);
}
/**
 * Contract "ERC20"
 * Purpose: Defining ERC20 standard with more advanced functionality like - Authorize spender to transfer EXH token
 */
function approve(address _spender, uint _value) public returns(bool ok);

//Add spender to authrize for spending specified amount of EXH Token