Add dr_libs (dr_flac, dr_mp3 and dr_wav) (#439)

* Add dr_libs (dr_flac, dr_mp3 and dr_wav)

* Fix dr_flac and dr_mp3

* Fix dr_mp3 package name

* Fix dr_flac again -_-

* Should be good now

packages/d/dr_flac/xmake.lua

@@ -0,0 +1,15 @@
+package("dr_flac")
+    set_homepage("https://github.com/mackron/dr_libs")
+    set_description("Single file audio decoding libraries for C/C++.")
+    set_license("MIT")
+
+    set_urls("https://github.com/mackron/dr_libs.git")
+    add_versions("0.12.29", "343aa923439e59e7a9f7726f70edc77a4500bdec")
+
+    on_install(function (package)
+        os.cp("dr_flac.h", package:installdir("include"))
+    end)
+
+    on_test(function (package)
+        assert(package:has_cfuncs("drflac_open", {includes = "dr_flac.h"}))
+    end)

packages/d/dr_mp3/xmake.lua

@@ -0,0 +1,15 @@
+package("dr_mp3")
+    set_homepage("https://github.com/mackron/dr_libs")
+    set_description("Single file audio decoding libraries for C/C++.")
+    set_license("MIT")
+
+    set_urls("https://github.com/mackron/dr_libs.git")
+    add_versions("0.6.27", "f357ade3aae55ced341aa7c83b4e7f628f948e51")
+
+    on_install(function (package)
+        os.cp("dr_mp3.h", package:installdir("include"))
+    end)
+
+    on_test(function (package)
+        assert(package:has_cfuncs("drmp3_init", {includes = "dr_mp3.h"}))
+    end)

packages/d/dr_wav/xmake.lua

@@ -0,0 +1,15 @@
+package("dr_wav")
+    set_homepage("https://github.com/mackron/dr_libs")
+    set_description("Single file audio decoding libraries for C/C++.")
+    set_license("MIT")
+
+    set_urls("https://github.com/mackron/dr_libs.git")
+    add_versions("0.12.19", "46f149034a9f27e873d2c4c6e6a34ae4823a2d8d")
+
+    on_install(function (package)
+        os.cp("dr_wav.h", package:installdir("include"))
+    end)
+
+    on_test(function (package)
+        assert(package:has_cfuncs("drwav_init_ex", {includes = "dr_wav.h"}))
+    end)