Add the possibility to use Matlab's namespace in model block

... or in steady_state_model block, where it should be possible to write something like:

 z = example.z_steadystate();

provided that the file +example/z_steadystate exists.

added preprocessor label

assigned to @houtanb

closed via commit preprocessor@9e454deb

mentioned in commit 4a1b5ecc

still need to add test for steady_state_model block

reopened

closed via commit 43c73a74

mentioned in commit 43c73a74