add Math library; change initial liquidity to geometric mean

contracts/Math.sol

@@ -0,0 +1,22 @@
+pragma solidity ^0.5.11;
+
+library Math {
+
+  function min(uint256 a, uint256 b) internal pure returns (uint256) {
+      return a < b ? a : b;
+  }
+
+  // based on https://github.com/ethereum/dapp-bin/pull/50/files#diff-2f78bfcc90b711a5c3bb69fd5b04f11aR28
+  function sqrt(uint256 x) internal pure returns (uint256) {
+    if (x == 0) return 0;
+    else if (x <= 3) return 1;
+    uint256 z = (x + 1) / 2;
+    uint256 y = x;
+    while (z < y) {
+        y = z;
+        z = (x / z + z) / 2;
+    }
+    return y;
+  }
+
+}