Add mixed quoter (#115)

Author: gretzke

.gitmodules

@@ -52,3 +52,6 @@
 [submodule "lib/openzeppelin-contracts"]
 	path = lib/openzeppelin-contracts
 	url = https://github.com/Openzeppelin/openzeppelin-contracts
+[submodule "src/pkgs/mixed-quoter"]
+	path = src/pkgs/mixed-quoter
+	url = https://github.com/Uniswap/mixed-quoter