Added option to change timestep for screen when below popup

Fixes #73

monarch/monarch.lua

@@ -1155,6 +1155,19 @@ function M.bottom(offset)
 	return screen and screen.id
 end
 
+
+--- Set the timestep to apply for a screen when below a popup
+-- @param id (string|hash) Id of the screen to change timestep setting for
+-- @param timestep (number) Timestep to apply
+function M.set_timestep_below_popup(id, timestep)
+	assert(id, "You must provide a screen id")
+	assert(timestep, "You must provide a timestep")
+	id = tohash(id)
+	assert(screens[id], ("There is no screen registered with id %s"):format(tostring(id)))
+	screens[id].timestep_below_popup = timestep
+end
+
+
 local function url_to_key(url)
 	return (url.socket or hash("")) .. (url.path or hash("")) .. (url.fragment or hash(""))
 end