ENH, CLN: When melt()'ing, allow for specification of custom variable and value names of the resulting DataFrame. Also fix indentation in melt() example to reflect actual output.
ENH: Add actual test assertions for melt().
DOC: Add documentation for new melt() functionality.
Merge pull request #3649 from hoechenberger/master

ENH: Allow for custom variable/value column names when melt()'ing