The contract based on ERC20.
The init params：
uint256 public totalSupply
string public name
string public symbol
uint public decimals transfer(address _to, uint256 _value)：Send _value tokens to _to from msg.sender
transferFrom(address _from, address _to, uint256 _value): Send _value tokens to _to from _from on the condition it is approved by _from
approve(address _spender, uint256 _value): msg.sender approves _spender to spend _value tokens on its behalf. This is a modified version of the ERC20 approve function to be a little bit safer
balanceOf(address _owner)：_owner The address that's balance is being requested
allowance(address _owner, address _spender)：This function makes it easy to read the allowed[] map