Maintenance: Update astyle version to 3.1 (#841)

Maintenance: Update astyle version to 3.1 (#841)

Version 2.04 is quite outdated now, and there are only minor
formatting differences with v3.1. All changes look to be good syntax.

Also, pass the astyle executable with command line option to
formater.pl. Avoiding environment variables which do not work on servers
with sanitized sub-shell environments such as our main server.