Added gunzip() wrapper to utils.system_tools
On-the-fly decompression of fits.Z
"Gracefully" fail on gzip unavailable
Improved gunzip() when gzip not available
gunzip() already returns the decompress file name
Also look for *.fits.Z in cache
Merge pull request #305 from jwoillez/eso_gunzip

On-the-fly decompression of downloaded fits.Z files
print_function in system_tools
redirect gzip -V stderr output to devnull (cc @jwoillez)
properly parse / override catalogue specification
added regression tests
Merge pull request #308 from keflavich/splatalogue_fixes

Bugfix: Splatalogue line list specification
added top20 and band selection
bugfixes, refactor to validate frequency ranges
minor docstringing
rename tests to indicate how little they test
Fix wording in docs page as suggested by @keflavich.
change install requirements
Skip doctest for download_list_of_fitsfiles
Merge pull request #309 from keflavich/splatalogue_top20

Add Top20 and Band (Basic) searching