Adding ReST source for the alpha-version of doc guidelines

doc/sphinx/dev_guide/documentation_guidelines.rst

+-------------------------------------------------------------------------------
+                        Documentation guidelines
+-------------------------------------------------------------------------------
+
+These guidelines are updated on the on-demand basis, covering only those issues
+that cause pains to the existing writers. At this point, we do not aim to come
+up with an exhaustive Documentation Style Guide for the Tarantool project. 
+
+===========================================================
+                        Markup issues
+===========================================================
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+                Wrapping text
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The limit is 80 characters per line for plain text, and no limit for any other
+constructions when wrapping affects ReST readability and/or HTML output. Also,
+it makes no sense to wrap text into lines shorter than 80 characters unless you
+have a good reason to do so.
+
+The 80-character limit comes from the ISO/ANSI 80x24 screen resolution, and it's
+unlikely that readers/writers will use 80-character consoles. Yet it's still a
+standard for many coding guidelines (including Tarantool). As for writers, the
+benefit is that an 80-character page guide allows keeping the text window rather
+narrow most of the time, leaving more space for other applications in a
+wide-screen environment.
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+              Making comments
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Sometimes we may need to leave comments in a ReST file. To make sphinx ignore
+some text during processing, use the following per-line notation with ".. //" as
+the comment marker:
+
+.. // your comment here
+
+`The notation example is excluded from HTML output, so please see the source in
+ReST.`
+
+The starting symbols ".. //" do not interfere with the other ReST markup, and
+they are easy to find both visually and using grep. There are no symbols to
+escape in grep search, just go ahead with something like this:
+
+  .. code-block:: console
+
+    grep ".. //" doc/sphinx/dev_guide/*.rst
+
+These comments don't work properly in nested documentation, though (e.g. if you
+leave a comment in module -> object -> method, sphinx ignores the comment and
+all nested content that follows in the method description).
+
+===========================================================
+                Language and style issues
+===========================================================
+
+*TBD (to be discussed)*
+
+===========================================================
+               Examples and templates
+===========================================================
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+               Module and function
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Here is an example of documenting a module (``my_fiber``) and a function 
+(``my_fiber.create``).
+
+.. module:: my_fiber
+
+.. function:: create(function [, function-arguments])
+
+    Create and start a ``my_fiber`` object. The object is created and begins to
+    run immediately.
+
+    :param function: the function to be associated with the ``my_fiber`` object
+    :param function-arguments: what will be passed to function
+
+    :return: created ``my_fiber`` object    
+    :rtype: userdata
+
+    **Example:**
+
+    .. code-block:: tarantoolsession
+
+        tarantool> my_fiber = require('my_fiber')
+        ---
+        ...
+        tarantool> function function_name()
+                 >   my_fiber.sleep(1000)
+                 > end
+        ---
+        ...
+        tarantool> my_fiber_object = my_fiber.create(function_name)
+        ---
+        ...
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+               Module, class and method
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Here is an example of documenting a module (``my_box.index``), a class
+(``my_index_object``) and a function (``my_index_object.rename``).
+
+.. module:: my_box.index
+
+.. class:: my_index_object
+    
+    .. method:: rename(index-name)
+
+        Rename an index.
+        
+        *Here follow 2 different notations for the same set of parameters.*
+                      
+        :param index_object: an object reference
+        :param index_name: a new name for the index (type = string)
+
+        Parameters:
+        
+        * :samp:`{index_object}` = an object reference;
+        * :samp:`{index-name}` (type = string) = new name for index.
+
+        :return: nil
+
+        Possible errors: index_object does not exist.
+
+        **Example:**
+
+        .. code-block:: tarantoolsession
+
+            tarantool> box.space.space55.index.primary:rename('secondary')
+            ---
+            ...
+
+        Complexity Factors: Index size, Index type, Number of tuples accessed.