Do _not_ update the doc (no user changes so far)

Do _not_ update the doc (no user changes so far)

This is a follow-up of the Python 3 port.
The `message` field is no longer supported in standard exceptions.

* Allow experiment and kind specific namelist templates
* 'DEFAULT.' prefix is optional but preferred
* Move pure template tests to new test case
* Add missing test for Revision 1.0.4 (allow uppercase in template name)

Searches experiment and mkexp path for relative file names