Updating contribution guidelines.

Clarifying style guidelines and refering "Writing Extensions" section.

doc/source/contributing.rst

@@ -4,10 +4,21 @@ Contributing Code
 
 We welcome code contributions via GitHub pull requests to the official WA
 repository. To help with maintainability of the code line we ask that the code
-uses a coding style consistent with the rest of WA code, which is basically
-`PEP8 <https://www.python.org/dev/peps/pep-0008/>`_ with line length and block
-comment rules relaxed (the wrapper for PEP8 checker inside ``dev_scripts`` will 
-run it with appropriate configuration).
+uses a coding style consistent with the rest of WA code. Briefly, it is
+
+- `PEP8 <https://www.python.org/dev/peps/pep-0008/>`_ with line length and block
+  comment rules relaxed (the wrapper for PEP8 checker inside ``dev_scripts`` 
+  will run it with appropriate configuration).
+- Four-space indentation (*no tabs!*).
+- Title-case for class names, underscore-delimited lower case for functions,
+  methods, and variables.
+- Use descriptive variable names. Delimit words with ``'_'`` for readability.
+  Avoid shortening words, skipping vowels, etc (common abbreviations such as
+  "stats" for "statistics", "config" for "configuration", etc are OK). Do
+  *not* use Hungarian notation (so prefer ``birth_date`` over ``dtBirth``).
+
+New extensions should also follow implementation guidelines specified in
+:ref:`writing_extensions` section of the documentation.
 
 We ask that the following checks are performed on the modified code prior to
 submitting a pull request:

doc/source/writing_extensions.rst

@@ -1,3 +1,5 @@
+.. _writing_extensions:
+
 ==================
 Writing Extensions
 ==================