New options for field name cleanup, tags, date field parsing to epoch_millis

[bitsofinfo]

Adds the following options

  --csv-clean-fieldnames          Strips double quotes and lower-cases all CSV
                                  header names for proper ElasticSearch
                                  fieldnames
  --csv-date-field TEXT           The CSV header name that represents a date
                                  string to parsed (via python-dateutil) into
                                  an ElasticSearch epoch_millis
  --csv-date-field-gmt-offset INTEGER
                                  The GMT offset for the csv-date-field (i.e.
                                  +/- N hours)
  --tags TEXT                     Custom static key1=val1,key2=val2 pairs to
                                  tag all entries with

[bitsofinfo]

Also includes #18 and #17

[Dzordre]

Could you provide an example about how to use your patch. I'm a bit lost with the new options ;)
Thanks.

[bitsofinfo]

used in: https://github.com/bitsofinfo/comms-analyzer-toolbox (but a fork of your project cause only my fork has the needed options submitted in this PR)