Fixes to the documentation presented when using the CLI.

PLEASE: Look over the changes before merging, to make sure they all look good.

_A summary of the changes_:
Fixes to README.rst:
-- fixed a mess-up in the example for "--glob", and a mess-up in the
   example for uploading
-- changed instructions for S3 keys from environmental variables to ia
   configure
-- changed the final example for "ia mine" to use "ia mine -"

Fixes to ia_list.py:
-- Changed the documentation for --columns to make it more obvious
   that any length list of comma separated columns was fine

Fixes to ia_metadata.py:
-- Fixed the doc on --exists, which somehow had some of it deleted

Fixes to ia_mine.py:
-- Mentioned in the usage that it can take stdin. Maybe that looks
   bad, though -- you decide.

Fixes to ia_search:
-- "--sort" can take multiple arguments. Added that to usage.

Multiple files:
-- Changed instructions to "pip install cython git+...=gevent"
   to just "pip install gevent" (which does work)