Initial commit of the fitshead script

Improved the help text

Improved the help messages and PEP8 compliance

Avoid crashing on a negative HDU extension number

Fixes Python 3 compatibility issue
Added support for EXTNAME/EXTVER HDU accessing and JSON output

removed JSON support; removed os.linesep; tolerate broken pipe errors
removed JSON support; removed os.linesep; tolerate broken pipe errors
Adds support for compressed headers + renamed to fitsheader
Adds support for compressed headers + renamed to fitsheader
Added documentation
Adds fitsheader script and documentation
Adds a test for the fitsheader script
Fixes sphinx build warnings
Fixes nitpicks; adds test for extname given in unicode
Fixes Python 3 syntax error
Renamed fitshead to fitsheader in CHANGES.rst
Fixes issue #2184
Removes workaround for issue #2184
Merge pull request #2092 from barentsen/add-fitshead-script

Add a `fitshead` script to display FITS headers