Write up the coding conventions

A document with the coding conventions must be available. They should include at least the PEP 8, PEP 256, maximum characters per line (90), new line character (UNIX's), TDD and other best practices (max indentation in a function: 3 levels; max statements per module: 200; etc). Finally, every source code file should have a link to this document in its header, after the copyright notice.