refactor max and min out of SafeMath

contracts/math/Math.sol

@@ -0,0 +1,24 @@
+pragma solidity ^0.4.11;
+
+/**
+ * @title Math
+ * @dev Assorted math operations
+ */
+
+contract Math {
+  function max64(uint64 a, uint64 b) internal constant returns (uint64) {
+    return a >= b ? a : b;
+  }
+
+  function min64(uint64 a, uint64 b) internal constant returns (uint64) {
+    return a < b ? a : b;
+  }
+
+  function max256(uint256 a, uint256 b) internal constant returns (uint256) {
+    return a >= b ? a : b;
+  }
+
+  function min256(uint256 a, uint256 b) internal constant returns (uint256) {
+    return a < b ? a : b;
+  }
+}