Tidy parallel output

In previous releases, some output unrelated to reporting test outcomes was being printed by all images. This release ensures all normal output comes from a single image, avoiding replication. Other than writes to an internal file (i.e., a string) and error termination stop codes, all printing/writing now happens via a call to the new one_image_prints subroutine.

What's Changed

• doc(README): update compiler support table/text by @rouson in #99
• Documentation: add app dir to ford.md & match project description to GitHib About text by @rouson in #100
• Chores by @rouson in #101
• Fix parallel testing: output only on image 1 by @rouson in #103
• fix(tests): output only on image 1 by @rouson in #102
• Feature: centralize output to one image by @rouson in #104
• Fix: workaround nagfor issue by @rouson in #106

Full Changelog: 3.1.0...3.1.1