Fixed:  + prefix doesn't work with ZipRecruiter; 404 on EmploymentGuide

-- Fixed:  + prefix on keywords doesn't work with ZipRecruiter; Needed
to be %2B

-- Fixed issue #23 - EmploymentGuide returns 404 pages if no results
are found for the keywords at that time.  Added a workaround in
JobsSitePlugin with a BUGBUG note for this one-off fix.
CareerCast: switched to 50 listings per page, better date filter