Update checker. (#251)

* Update checker.

* Fix build and enum class.

* Get rid of submodule for httplib.

* Get rid of submodule for curl.

* Minor style changes and fix video.cpp Linux build error.

* CTitleStateIntro_patches: implemented update message

* Update update_checker.cpp

* CTitleStateIntro_patches: fix fade out accepting input

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Co-authored-by: Hyper <34012267+hyperbx@users.noreply.github.com>

.gitmodules

@@ -61,3 +61,6 @@
 [submodule "thirdparty/implot"]
 	path = thirdparty/implot
 	url = https://github.com/epezent/implot.git
+[submodule "thirdparty/json"]
+	path = thirdparty/json
+	url = https://github.com/nlohmann/json