Add a --fields function to expand search beyond body fields.

This needs to include other rich text fields besides the standard field_body field. A option to identify fields to search and update would be helpful such as --fields=[comma,separated,list,of,fields] will not only include the field_body but other fields you submit to check for the files and update any references to them. So if you also have a field called field_sidebar, and field_highlight, you'd enter
--fields=field_sidebar,field_highlight.

Alternatively this could include all fields in the database identified as full text since this can only be run once for any given file.