Update doc style

We use RST everywhere, which dictates most of the style, so the styles mentioned previously were either obsolete or inaccurate. Updated the doc to be clearer on things which RST does not specify/care about.

meta/documentation_style.rst

@@ -1,43 +1,45 @@
-===================
 Documentation Style
 ===================
 
 A brief single sentence to describe what this file contains; in this case a
 description of the style to write documentation in.
 
+Format
+------
 
-Sections
-========
-
-Each section should be separated from the others by two blank lines. Headings
-should be underlined using a row of equals signs (===). Paragraphs should be
-separated by a single blank line, and wrap to no further than 80 columns.
+We use restructured text throughout all the documentation. You should NOT use
+markdown (github-flavored or otherwise). This format was chosen partly because
+Sphinx only supports RST.
 
-[[TODO(username): if you want to leave some unanswered questions, notes for
-further consideration, or other kinds of comment, use a TODO section. Make sure
-to notate it with your name so we know who to ask about it!]]
 
-Subsections
------------
+Sections
+--------
 
-If required, subsections can use a row of dashes to underline their header. A
-single blank line between subsections of a single section.
+RST support lots of different punctuation characters for underlines on sections.
+Content in the specification MUST use the same characters in order for the
+complete specification to be merged correctly. These characters are:
 
+- ``=`` : Top-level sections
+- ``-`` : Second-level sections
+- ``~`` : Third-level sections
+- ``+`` : Fourth-level sections
+- You should rethink your document layout if you require a fifth level.
 
-Bullet Lists
-============
+TODOs
+-----
 
- * Bullet lists can use asterisks with a single space either side.
- 
- * Another blank line between list elements.
+Any RST file in this repository may make it onto ``matrix.org``. We do not want
+``TODO`` markers visible there. For internal comments, notes, TODOs, use standard
+RST comments like so::
 
+  .. TODO-Bob
+    There is something to do here. This will not be rendered by something like
+    rst2html.py so it is safe to put internal comments here.
 
-Definition Lists
-================
+You SHOULD put your username with the TODO so we know who to ask about it.
 
-Terms:
-  Start in the first column, ending with a colon
+Line widths
+-----------
 
-Definitions:
-  Take a two space indent, following immediately from the term without a blank
-  line before it, but having a blank line afterwards.
+We use 80 characters for line widths. This is a guideline and can be flouted IF
+AND ONLY IF it makes reading more legible. Use common sense.