Feature: find a way how we can use power of Sphinx to document violations

[sobolevn]

Currently we have two hacks:

1. error code is explicitly duplicated in the docs
2. each error template is prefixed by #: so it would appear in the final html

But, I do not like this solution. There must be a better way!

What can be done?

1. We can try to make error_code and error_template default arguments for all classes
2. We can try to make a custom directive
3. We can try to locally configure things we need to show to the user
4. We can explicitly add these fields to all autoclass lines (I do not like it)