docs: Better _mssql.MSSQLStoredProcedure.bind() documentation.

Fixes #176.

docs/ref/_mssql.rst

@@ -320,25 +320,25 @@ Functions
    This method binds a parameter to the stored procedure. *value* and *dbtype*
    are mandatory arguments, the rest is optional.
 
-   :param value: Is the value to store in the parameter
+   :param value: Is the value to store in the parameter.
 
    :param dbtype: Is one of: ``SQLBINARY``, ``SQLBIT``, ``SQLBITN``,
                   ``SQLCHAR``, ``SQLDATETIME``, ``SQLDATETIM4``,
                   ``SQLDATETIMN``, ``SQLDECIMAL``, ``SQLFLT4``, ``SQLFLT8``,
                   ``SQLFLTN``, ``SQLIMAGE``, ``SQLINT1``, ``SQLINT2``,
                   ``SQLINT4``, ``SQLINT8``, ``SQLINTN``, ``SQLMONEY``,
                   ``SQLMONEY4``, ``SQLMONEYN``, ``SQLNUMERIC``, ``SQLREAL``,
-                  ``SQLTEXT``, ``SQLVARBINARY``, ``SQLVARCHAR``, ``SQLUUID``
+                  ``SQLTEXT``, ``SQLVARBINARY``, ``SQLVARCHAR``, ``SQLUUID``.
 
-   :param name: Is the name of the parameter
+   :param name: Is the name of the parameter. Needs to be in ``"@name"`` form.
 
-   :param output: Is the direction of the parameter: ``True`` indicates that it
-                   is also an output parameter that returns value after
-                   procedure execution
+   :param output: Is the direction of the parameter. ``True`` indicates that it
+                  is an output parameter i.e. it returns a value after procedure
+                  execution (in SQL DDL they are declared by using the
+                  ``"output"`` suffix, e.g. ``"@aname varchar(10) output"``).
 
-   :param null: TBD
-
-   .. todo:: Document ``null`` ``MSSQLStoredProcedure.bind()`` argument.
+   :param null: Boolean. Signals than NULL must be the value to be bound to the
+                argument of this input parameter.
 
    :param max_length: Is the maximum data length for this parameter to be
                       returned from the stored procedure.