Hi,
same problem here: Installed the plugin but nothing happens (only the picturefill.js is included in frontend).
I have no settings-page nor link to settingspage in the backend: looked through your code and couldn’t find any kind of add_menu command …
shouldn’t there be one?
No srcsets created.
Can you help?
i use WP 4.3.1 and php 5.4 – if this matters.