nmd: add package (#3965)

* nmd: add package

* nmd: improve description and add license

* nmd: set headeronly

* nmd: fix license

packages/n/nmd/xmake.lua

@@ -0,0 +1,22 @@
+package("nmd")
+    set_kind("library", {headeronly = true})
+    set_homepage("https://github.com/Nomade040/nmd")
+    set_description("An x86 assembler and disassembler along with a C89 header file (nmd_assembly.h), and a C89 2D graphics library (nmd_graphics.h).")
+    set_license("Unlicense")
+
+    add_urls("https://github.com/Nomade040/nmd.git")
+    add_versions("2021.03.28", "33ac3b62c7d1eb28ae6b71d4dd78aa133ef96488")
+
+    on_install(function (package)
+        os.cp("nmd_assembly.h", package:installdir("include/nmd"))
+        os.cp("nmd_graphics.h", package:installdir("include/nmd"))
+    end)
+
+    on_test(function (package)
+        assert(package:check_cxxsnippets({test = [[
+            #include <nmd/nmd_assembly.h>
+            void test() {
+                nmd_x86_instruction instruction;
+            }
+        ]]}, {configs = {languages = "c89"}}))
+    end)