Fix documentation in function _copy_data(). WONTFIX hanging FD problem #1921

 * Won't fix hanging file descriptor problem due to this problem requiring a
   complete rewrite of nearly every function in the module.
 * Closes #1921, #1927, #1929.
 * Fix whitespace styling.
Fix blanket case except statement in _copy_data().

 * Fixes #1922.
Fix documentation in GPG._handle_io().
Merge branch 'fix/1921-1927-1929-hanging-fds' into development