Generate example documentation from code

Bug report

What happened / Problem description: The python script to extract the code documentation of the examples, generate_example_docs.py, or something within the generation of the example documentation in general is broken.

What you expected to happen: Executing the script should generate the markdown documents. Instead, I get an error message: File "generate_example_docs.py", line 131, in generateReadme(abspath) File "generate_example_docs.py", line 115, in generateReadme except FileNotFoundError: NameError: global name 'FileNotFoundError' is not defined

when checking the script, this error message seems to relate to the .doc_config files. However, I checked and all examples have a .doc_config file.

How to reproduce it (as minimally and precisely as possible): I discovered this while working on the documentation for the new pnm example, but even on the current master, I get the identical error message, also when working on my PC in the office, see the error message above

Environment:

• Dune version: 2.7 (both PC and laptop)
• DuMux version: master, feature/pnm-example branch (both PC and laptop)
• Python version: 2.7.13 (laptop, no idea about PC)