Add default ftoptions plugin to override settings

The ftoptions plugin will override values in settings.json based
on language requirements (e.g. using tabs in makefiles).

runtime/plugins/ftoptions/ftoptions.lua

@@ -0,0 +1,9 @@
+function onViewOpen(view)
+    local ft = view.Buf.Settings["filetype"]
+
+    if ft == "makefile" or ft == "go" then
+        SetOption("tabstospaces", "off")
+    elseif ft == "python" then
+        SetOption("tabstospaces", "on")
+    end
+end