add rxcpp (#2102)

* add rxcpp

* Update xmake.lua

---------

Co-authored-by: ruki <waruqi@gmail.com>

packages/r/rxcpp/xmake.lua

@@ -0,0 +1,28 @@
+package("rxcpp")
+    set_kind("library", {headeronly = true})
+    set_homepage("http://reactivex.io/RxCpp/")
+    set_description("Compose async and event-based programs using observable sequences and LINQ-style query operators.")
+    set_license("Apache-2.0")
+
+    set_urls("https://github.com/ReactiveX/RxCpp.git")
+    add_versions("v4.1.1", "90758767f7299ff94ba7f359944fde479a7aeb92")
+    add_versions("v3.0.0", "8290f92f744f807e83b1bfe9e8c0ffd162140ec8")
+
+    on_install(function(package)
+        os.cp("Rx/v2/src/rxcpp", package:installdir("include"))
+    end)
+
+    on_test(function(package)
+        assert(package:check_cxxsnippets({test = [[
+            #include <rxcpp/rx.hpp>
+            #include <iostream>
+
+            void test() {
+                auto values1 = rxcpp::sources::range(1, 5);
+                values1.subscribe(
+                    [] (int v) { std::cout << "OnNext: " << v << "\n"; },
+                    [] () { std::cout << "OnCompleted\n"; }
+                );
+            }
+        ]]}, {configs = {languages = "c++11"}}))
+    end)