Examples in the API documentation

[Luthaf]

The API documentation is complete, but lacks examples. Most of the function could get some examples.

• energy module;
• sim module;
• sys module;
• out module;
• types module;

[Luthaf]

Tagging L-Easy as this can be an easy first contribution to the code. Pick a function missing example, check for usage in the code/unit tests and write the example.