Add hardlink generators for LICENSE and README.md to testpath

Git does not handle links, by creating hardlinks, the files will be included in any sdist operations.
.gitignore: Add the LICENSE, README.md hardlinks
gkeys/checks.py: Correctly set the exiry to 5 years (glep 63)
gkeys/config.py: Fix the config defaults to do % substitution for the defaults

If it did not find and loada valid config file, the defaults did not have the % subtitution applied.
The logger calls were not using the logger setting in the config. So I changed that
gkeys/config.py: Subclass ConfigParser to be able to set defaults in the config

Allow some base defaults to be set in the [base] section of the config.
Reset our defaults from those changes.
Resave the new defaults back to the configparser for interpolation when retrieving the values.
gkeys/base.py: Make the category/seedfile choices dynamic
gkeys/lib.py: fix a missed mode setting for an ensure_dirs() call
gkeys: Use the new category handling system
gkeys/actions.py: Add a listcats action
gkeys/actions.py: Improve category error message
gkeys/actions.py: Fix listseed action for the new category/seedfile handling
gkeys/etc/gkeys.conf.sample: Update for new category/seedfile handling