Add hashtag option

[janboddez]

Add a regular setting for including hashtags.

These should be appended before the old content filter is run, so as to avoid duplicate hashtags/let the filter override everything.

[janboddez]

This is going to be covered by the template tag thingy. So rather than have a bunch of checkboxes of what to include (or use the existing hook), users (well, site administrators) will be able to store a "template," complete with template tags (%title%, %tags%, etc.) and all.