add basic tokens

contracts/ERC20.sol

+contract ERC20 {
+    function totalSupply() constant returns (uint);
+    function balanceOf(address who) constant returns (uint);
+    function allowance(address owner, address spender) constant returns (uint);
+
+    function transfer(address to, uint value) returns (bool ok);
+    function transferFrom(address from, address to, uint value) returns (bool ok);
+    function approve(address spender, uint value) returns (bool ok);
+
+    event Transfer(address indexed from, address indexed to, uint value);
+    event Approval(address indexed owner, address indexed spender, uint value);
+}

contracts/Token.sol

+// Source: https://github.com/nexusdev/erc20
+// Flat file implementation of `dappsys/token/base.sol::DSTokenBase`
+
+// Everything throws instead of returning false on failure.
+import 'ERC20.sol';
+
+contract Token is ERC20
+{
+    mapping( address => uint ) _balances;
+    mapping( address => mapping( address => uint ) ) _approvals;
+    uint _supply;
+
+    function Token( uint initial_balance ) {
+        _balances[msg.sender] = initial_balance;
+        _supply = initial_balance;
+    }
+    function totalSupply() constant returns (uint supply) {
+        return _supply;
+    }
+    function balanceOf( address who ) constant returns (uint value) {
+        return _balances[who];
+    }
+    function transfer( address to, uint value) returns (bool ok) {
+        if( _balances[msg.sender] < value ) {
+            throw;
+        }
+        if( !safeToAdd(_balances[to], value) ) {
+            throw;
+        }
+        _balances[msg.sender] -= value;
+        _balances[to] += value;
+        Transfer( msg.sender, to, value );
+        return true;
+    }
+    function transferFrom( address from, address to, uint value) returns (bool ok) {
+        // if you don't have enough balance, throw
+        if( _balances[from] < value ) {
+            throw;
+        }
+        // if you don't have approval, throw
+        if( _approvals[from][msg.sender] < value ) {
+            throw;
+        }
+        if( !safeToAdd(_balances[to], value) ) {
+            throw;
+        }
+        // transfer and return true
+        _approvals[from][msg.sender] -= value;
+        _balances[from] -= value;
+        _balances[to] += value;
+        Transfer( from, to, value );
+        return true;
+    }
+    function approve(address spender, uint value) returns (bool ok) {
+        _approvals[msg.sender][spender] = value;
+        Approval( msg.sender, spender, value );
+        return true;
+    }
+    function allowance(address owner, address spender) constant returns (uint _allowance) {
+        return _approvals[owner][spender];
+    }
+    function safeToAdd(uint a, uint b) internal returns (bool) {
+        return (a + b >= a);
+    }
+}