educe.util.concat and concat_l

I keep reusing these silly little functions
Naming concision for a simple concept here matters to me
refactor uses of concat function
educe.util: more powerful flag selection

* add_corpus_filters now supports a choice_fields
  arg (:: Dict String String) that lets you limit
  a field to a particular subset
  (eg. you can only choose from GOLD or SILVER here)

* without_fields lets you specify corpus selection
  fields to knock out

* mk_is_interesting lets you 'preselect' the value
  for some fields (eg. is interesting if the stage
  is discourse)
refactor stac corpus arg parsing

Refactor STAC CLI corpus selection
educe.util: oops
Replace fuzzy requirement by soundex package

Fuzzy involves some C compilation bits which seems to make
installation more difficult than necessary.