Clean up lua docs scripts

- ldoc is now a git submodule
- ldoc can be installed using scripts/install.{sh,ps1}
- lua docs can be build using scripts/build.{sh,ps1}
- all lua docs-related files now reside inside of the docs folder

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "Libraries/moonsharp"]
 	path = Libraries/moonsharp
 	url = https://github.com/evilfactory/moonsharp.git
+[submodule "docs/libs/ldoc"]
+	path = docs/libs/ldoc
+	url = https://github.com/impulsh/LDoc.git