add tests for configurable default values for parameters

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
implement configurable default values for parameters

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
document new feature: configurable default values for parameters

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
+hint

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>
Merge branch 'feature/default_parameters' of https://github.com/asteven/cdist
changes(2.3.3)++

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>