Firstly, thank you for this library. It's seriously impressive and so useful! I ran into an exception when working with the `is_running` function: ``` File "quip.py", line 40, in main if is_running('update'): File "/Users/orf/PycharmProjects/alfred-quip-workflow/workflow/background.py", line 99, in is_running pid = int(file_obj.read().strip()) ValueError: invalid literal for int() with base 10: '' ``` The code is taken from the getting started guide and isn't doing anything crazy: ``` if not wf.cached_data_fresh('documents', max_age=60 * 60 * 60): cmd = ['/usr/bin/python', wf.workflowfile('quip-update.py')] run_in_background('update', cmd) if is_running('update'): wf.add_item('Getting new posts from Pinboard', valid=False, icon=ICON_INFO) ``` I haven't dug into it, but it seems to me like it's a race condition where the file is created by the new process but the pid has not been written to it yet. Using something like the `pidfile` library solves a lot of these issue, could you vendor it inside this library?