Add ERC20 interface

ERC20Interface.sol

@@ -0,0 +1,21 @@
+contract ERC20Interface {
+
+    string public constant name = "Token Name";
+    string public constant symbol = "SYM";
+    uint8 public constant decimals = 18;  // 18 is the most common number of decimal places
+    // 0.0000000000000000001  个代币
+
+    function totalSupply() public constant returns (uint);
+
+    function balanceOf(address tokenOwner) public constant returns (uint balance);
+
+    function allowance(address tokenOwner, address spender) public constant returns (uint remaining);
+    function approve(address spender, uint tokens) public returns (bool success);
+
+    function transfer(address to, uint tokens) public returns (bool success);
+    function transferFrom(address from, address to, uint tokens) public returns (bool success);
+
+
+    event Transfer(address indexed from, address indexed to, uint tokens);
+    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
+}