ESO core cleanup, plus a refactor of the file downloader to allow
progressbar and chunked reading
use requests directly rather than going through AstroResponse, which
causes problems
fix tests: need to accept `stream` keyword
astroresponse needs to take stream keyword.  Not obvious that it will
use it appropriately though.
factor out _print_help and add a new APEX query tool.  Also, fix some
caching failures from earlier
progressbar works now
fix URLs in ESO apex help
Merge pull request #399 from keflavich/download_file_refactor

base query & ESO file downloads chunked