Remove call to write the GPG secret key passphrase into the logger.
Make GnuPG process attribute private in parser classes.
Cleanup coding style and docstrings in old module code.
Add gnupg options sanitising function.
Separate lstat filesize checking assertion into a seperate function.
Separate the regex shell escape find and replace, and quote wrapping logic,
into a separate function.
Separate function for switching option hyphenation to underscores for
assignment to object attributes.
Whitespace fix.
Separate out logic for determining if a GPG option is allowed.

 * Add function _is_allowed().
 * Update documentation for _is_allowed() and _sanitise().
Update documentation for function _sanitise().
Update documentation for function _is_allowed().
Add calls to _underscore() in _is_allowed() to avoid repeating the call in
other functions.
Rewrite function _sanitise() with calls to other new check functions().

 * Remove function _type_check_and_remove_escapes().
Update documentation for function _sanitise().
Merge branch 'fix/1747-remove-popen-with-shell' into development
Add encrypted copy of notes from my audit.
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