Cmake love (#55)

* Do CMake properly

* Remove uneeded file

* Add patch to version

* Init submodule in appveyor

* Use FetchContent

* Up CMake version requirement

* Use Xenial on Travis instead of Trusty

* Tidy traits

* Use Xenial repos

tests/assignment.cpp

@@ -1,5 +1,5 @@
 #include "catch.hpp"
-#include "expected.hpp"
+#include <tl/expected.hpp>
 
 TEST_CASE("Simple assignment", "[assignment.simple]") {
   tl::expected<int, int> e1 = 42;