Vendor raptor source files (was embedded gitlink)

Tree vendored at upstream 0019c5dd; origin + license recorded in
raptor/VENDOR.txt. Windows SDL dev packages excluded via .gitignore.

raptor/.gitignore

@@ -0,0 +1,8 @@
+output.map
+CMakeFiles
+cmake_install.cmake
+CMakeCache.txt
+Makefile
+build
+.vscode
+**/.DS_Store