Remove trailing whitespace in source code

There's a bunch of trailing whitespace in the parseargs source. I suppose a proper fix involves filtering the tree to pretend it was never introduced. Extra-low priority.

Locate the parseargs source files and inspect the reported trailing whitespace. Remove the whitespace throughout the source, then review the resulting diff to confirm that it contains only whitespace cleanup and that no trailing whitespace remains.

Written by the indexing model from the issue text.