Added support for inputting units
Added test for units and corresponding data file
Removed unnecessary statement
Added support for inputting column description as well
Included test file in setup_package
Changed SExtractor test to include a description check
Made SExtractor regex verbose, enhanced test and test file
Added changelog entry
Fixed regex to allow for units without description, adjusted test accordingly
Merge pull request #2372 from amras1/sextractor-units

Added support for inputting description and units in io.ascii.SExtractor