Add tl::expected (#200)

* Add tl::expected

* Update xmake.lua

* Update xmake.lua

packages/e/expected/xmake.lua

@@ -0,0 +1,23 @@
+package("expected")
+
+    set_homepage("https://github.com/TartanLlama/expected")
+    set_description("C++11/14/17 std::expected with functional-style extensions")
+    set_license("CC0")
+
+    set_urls("https://github.com/TartanLlama/expected/archive/$(version).zip",
+             "https://github.com/TartanLlama/expected.git")
+
+    add_versions("v1.0.0", "c1733556cbd3b532a02b68e2fbc2091b5bc2cccc279e4f6c6bd83877aabd4b02")
+
+    on_install(function (package)
+        os.cp("include/tl", package:installdir("include"))
+    end)
+
+    on_test(function (package)
+        assert(package:check_cxxsnippets({test = [[
+            void test()
+            {
+                tl::expected<int, int> e1 = 42;
+            }
+        ]]}, {configs = {languages = "c++11"}, includes = { "tl/expected.hpp"} }))
+    end)