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

Currently for lists only

* set build subdir default to empty (was 'build')
* add option to ignore errors when executing the script (allows missing files)
* add help option
* add option to set build directory explicitly (eg for mtime)
* add support for scripts in current directory
* make support for non-ksh here documents more robust (checks for actual shell)

Fixes long run times for extended jobs/namelist groups