Doc: Generate documentation with Sphinx

HTML documentation should be built with sphinx. This enables easy
integration with Read The Docs [1]. It can also be generated manually by
running:

    make -C docs html

A man page can be generated by running:

    make -C docs man

[1]: http://yamllint.readthedocs.org/

docs/rules.rst

@@ -0,0 +1,90 @@
+Rules
+=====
+
+When linting a document with yamllint, a series of rules (such as
+``line-length``, ``trailing-spaces``, etc.) are checked against.
+
+A :doc:`configuration file <configuration>` can be used to enable or disable
+these rules, to set their level (*error* or *warning*), but also to tweak their
+options.
+
+This page describes the rules and their options.
+
+.. contents:: List of rules
+   :local:
+   :depth: 1
+
+braces
+------
+
+.. automodule:: yamllint.rules.braces
+
+brackets
+--------
+
+.. automodule:: yamllint.rules.brackets
+
+colons
+------
+
+.. automodule:: yamllint.rules.colons
+
+commas
+------
+
+.. automodule:: yamllint.rules.commas
+
+comments
+--------
+
+.. automodule:: yamllint.rules.comments
+
+comments-indentation
+--------------------
+
+.. automodule:: yamllint.rules.comments_indentation
+
+document-end
+------------
+
+.. automodule:: yamllint.rules.document_end
+
+document-start
+--------------
+
+.. automodule:: yamllint.rules.document_start
+
+empty-lines
+-----------
+
+.. automodule:: yamllint.rules.empty_lines
+
+hyphens
+-------
+
+.. automodule:: yamllint.rules.hyphens
+
+indentation
+-----------
+
+.. automodule:: yamllint.rules.indentation
+
+line-length
+-----------
+
+.. automodule:: yamllint.rules.line_length
+
+new-line-at-end-of-file
+-----------------------
+
+.. automodule:: yamllint.rules.new_line_at_end_of_file
+
+new-lines
+---------
+
+.. automodule:: yamllint.rules.new_lines
+
+trailing-spaces
+---------------
+
+.. automodule:: yamllint.rules.trailing_spaces