facemask-plugin: Add Facemask Plugin

The Facemask Plugin allows users to overlay a mask over a source that contains face(s) using a standard obs filter.

Merges #12

.gitmodules

@@ -20,3 +20,6 @@
 	path = plugins/obs-ndi
 	url = https://github.com/stream-labs/obs-ndi.git
 	branch = streamlabs-obs
+[submodule "plugins/facemask-plugin"]
+	path = plugins/facemask-plugin
+	url = https://github.com/stream-labs/facemask-plugin.git

plugins/CMakeLists.txt

@@ -21,6 +21,11 @@ if(WIN32)
 	else()
 		message(STATUS "enc-amf submodule not found!  Please fetch submodules.  enc-amf plugin disabled.")
 	endif()
+	if (EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/facemask-plugin/CMakeLists.txt")
+		add_subdirectory(facemask-plugin)
+	else()
+		message(STATUS "facemask-plugin submodule not found!  Please fetch submodules.  facemask-plugin plugin disabled.")
+	endif()
 	if (MSVC)
 		add_subdirectory(win-ivcam)
 	endif()