fixing gzip import issue 2774
Code now import both astropy and system gzip

For clarity the astropy gzip is called _astropy_gzip
and the system gzip is called _system_gzip.

All gzip.x statements have been changed to use the
_astropy_gzip.

All isinstances statements check both
Allow format specificiers as Column format strings & deal with masked values.
Also refactored the string tests, and added regression test against formatting
of np.float32, etc.  Because masked values now are OK: [closes #1026]
creating global variable with the two GzipFile types
Added test for gzip file suggested by Erik Bray.
adding issue 2783 to the changelog for 0.4.2
Merge pull request #2783 abostroem/gzip_fix
Add several FAQs concerning performance
Add mention of the license to the readme
Added affiliated package release instructions
Syntax fixes
Don’t use NamedTemporaryFile for show_in_browser, since it gets deleted as soon as it is no longer referenced. Instead create a temporary directory and place a file inside.
Merge pull request #2911 from eteq/add-astropy-license

Add mention of the license to the readme
Added jsfiles, cssfiles, and js option to HTML writer
Re-use io.ascii html writer in jsviewer writer
Use local js and css files by default when using show_in_browser
Added changelog entry
Fix failing HTML tests
Fix another failing HTML test
Added unit test for jsviewer writer