[TH] exit process when an error occurs

Seems to help prevent the never-ending processing 
feed.
[TH] convert NaN to 0 errorCount

Not entirely sure this is what is a good solution,
because it’s unclear why NaN comes through, but
it allows the feed to finish processing.
[TH] manually trigger overview processing

Added in code so you can manually trigger an
overview processing for debugging purposes. It
doesn’t play nicely with the way overview
processing is typically triggered, commenting out 
to be used as needed.
[TH] clean up debugging entry point
Merge pull request #223 from votinginfoproject/error-count-feed-processing

Error count feed processing