ThirdParty: Add optional-lite polyfill

Thanks to all who have made contributions to
https://github.com/martinmoene/optional-lite

third-party/optional-lite/.gitignore

@@ -0,0 +1,47 @@
+# Compiled Object files
+*.slo
+*.lo
+*.o
+*.obj
+
+# Precompiled Headers
+*.gch
+*.pch
+
+# Compiled Dynamic libraries
+*.so
+*.dylib
+*.dll
+
+# Fortran module files
+*.mod
+
+# Compiled Static libraries
+*.lai
+*.la
+*.a
+*.lib
+
+# Executables
+*.exe
+*.out
+*.app
+
+# Buck
+/buck-out/
+/.buckd/
+/buckaroo/
+.buckconfig.local
+BUCKAROO_DEPS
+
+# Build folder
+/build/
+
+# CodeBlocks IDE files
+*.layout
+
+# Visual Studio Code
+/.vscode/
+
+# Visual Studio
+/.vs/