libs: add vim modeline

Signed-off-by: Julien Danjou <julien@danjou.info>

lib/awful.lua.in

@@ -1178,3 +1178,5 @@ hooks.focus.register(titlebar.update)
 hooks.unfocus.register(titlebar.update)
 hooks.titleupdate.register(titlebar.update)
 hooks.unmanage.register(titlebar.remove)
+
+-- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:encoding=utf-8:textwidth=80

lib/beautiful.lua

@@ -73,3 +73,5 @@ function init(path)
 end
 
 setmetatable(package.loaded[module_name], package.loaded[module_name])
+
+-- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:encoding=utf-8:textwidth=80

lib/tabulous.lua

@@ -250,3 +250,5 @@ end
 
 -- Set up hook so we don't leave lost hidden clients
 awful.hooks.unmanage.register(untab)
+
+-- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:encoding=utf-8:textwidth=80