Create third_party folder, note it in the license text

LICENSE.md

@@ -6,7 +6,7 @@ This repo contains the source code for VVVVVV, including all level content and t
 
 If you are interested in distributing work that falls outside the terms in the licence below, or if you are interested in distributing work that includes using any part of VVVVVV not included in this repo then please get in touch - we can discuss granting a licence for that on a case by case basis. The purpose of making the contents of this repo available is for others to learn from, to inspire new work, and to allow the creation of new tools and modifications for VVVVVV.
 
-This software available from here is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any claim, damages or other liability arising from the use or in connection with this software. All materials in the repo are copyright of Terry Cavanagh © 2010-2020.
+This software available from here is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any claim, damages or other liability arising from the use or in connection with this software. All materials in the repo, with the exception of the contents of the "third_party" directory, are copyright of Terry Cavanagh © 2010-2020.
 
 Permission is granted to anyone to use this software and to alter it and redistribute it freely, subject to the following restrictions:
 

desktop_version/CMakeLists.txt

@@ -51,7 +51,12 @@ IF(NOT WIN32)
 ENDIF()
 
 # Include Directories
-INCLUDE_DIRECTORIES(src tinyxml physfs lodepng)
+INCLUDE_DIRECTORIES(
+	src
+	../third_party/tinyxml
+	../third_party/physfs
+	../third_party/lodepng
+)
 
 # Source Lists
 SET(VVV_SRC
@@ -89,27 +94,27 @@ SET(VVV_SRC
 	src/SteamNetwork.c
 )
 SET(XML_SRC
-	tinyxml/tinystr.cpp
-	tinyxml/tinyxml.cpp
-	tinyxml/tinyxmlerror.cpp
-	tinyxml/tinyxmlparser.cpp
+	../third_party/tinyxml/tinystr.cpp
+	../third_party/tinyxml/tinyxml.cpp
+	../third_party/tinyxml/tinyxmlerror.cpp
+	../third_party/tinyxml/tinyxmlparser.cpp
 )
 SET(PFS_SRC
-	physfs/physfs.c
-	physfs/physfs_archiver_dir.c
-	physfs/physfs_archiver_unpacked.c
-	physfs/physfs_archiver_zip.c
-	physfs/physfs_byteorder.c
-	physfs/physfs_unicode.c
-	physfs/physfs_platform_posix.c
-	physfs/physfs_platform_unix.c
-	physfs/physfs_platform_windows.c
+	../third_party/physfs/physfs.c
+	../third_party/physfs/physfs_archiver_dir.c
+	../third_party/physfs/physfs_archiver_unpacked.c
+	../third_party/physfs/physfs_archiver_zip.c
+	../third_party/physfs/physfs_byteorder.c
+	../third_party/physfs/physfs_unicode.c
+	../third_party/physfs/physfs_platform_posix.c
+	../third_party/physfs/physfs_platform_unix.c
+	../third_party/physfs/physfs_platform_windows.c
 )
 IF(APPLE)
 	# Are you noticing a pattern with this Apple crap yet?
-	SET(PFS_SRC ${PFS_SRC} physfs/physfs_platform_apple.m)
+	SET(PFS_SRC ${PFS_SRC} ../third_party/physfs/physfs_platform_apple.m)
 ENDIF()
-SET(PNG_SRC lodepng/lodepng.c)
+SET(PNG_SRC ../third_party/lodepng/lodepng.c)
 
 # Executable information
 IF(WIN32)