Added contracts/token/BurnableToken.sol

contracts/token/BurnableToken.sol

+pragma solidity ^0.4.13;
+
+import './StandardToken.sol';
+
+/**
+ * @title Burnable Token
+ * @dev Token that can be irreversibly burned (destroyed).
+ */
+contract BurnableToken is StandardToken{
+
+    /**
+     * @dev Burns a specific amount of tokens.
+     * @param _value The amount of token to be burned.
+     */
+    function burn(uint _value)
+        public
+    {
+        require(_value > 0);
+
+        address burner = masg.sender;
+        balances[burner] = balanced[burner].sub(_value);
+        totalSupply = totalSupply.sub(_value);
+        Burn(burner, _value);
+    }
+
+    event Burn(address indexed burner, uint indexed value);
+}
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