feat(lua): low-level interpreter mode (nvim -ll)

runtime/doc/starting.txt

@@ -239,6 +239,14 @@ argument.
 		Disables |shada| unless |-i| was given.
 		Disables swapfile (like |-n|).
 
+							*-ll*
+-ll {script} [args]
+		Execute a lua script, similarly to |-l|, but the editor is not
+		initialized. This gives a lua enviroment similar to a worker
+		thread. See |lua-loop-threading|.
+
+		Unlike `-l` no prior arguments are allowed.
+
 							*-b*
 -b		Binary mode.  File I/O will only recognize <NL> to separate
 		lines.  The 'expandtab' option will be reset.  The 'textwidth'