Add documentation for typealiases module.

docs/index.rst

@@ -7,6 +7,7 @@ Contents:
    :maxdepth: 2
 
    instances
+   typealiases
    references
 
 Indices and tables

docs/typealiases.rst

+============
+Type Aliases
+============
+
+.. module:: yangson.typealiases
+   :synopsis: Type aliases
+.. moduleauthor:: Ladislav Lhotka <lhotka@nic.cz>
+
+We define several type aliases shown in the following table to give more meaning to type hints [PEP484].
+
++----------------+--------------------------------------------------------------+--------+
+| Alias          | Type                                                         | Remark |
++================+==============================================================+========+
+| Uri            | :class:`str`                                                 | (1)    |
++----------------+--------------------------------------------------------------+--------+
+| YangIdentifier | :class:`str`                                                 | (2)    |
++----------------+--------------------------------------------------------------+--------+
+| RevisionDate   | ``Optional[``:class:`str```]``                               | (3)    |
++----------------+--------------------------------------------------------------+--------+
+| Value          | Union[:class:`int`, :class:`str`, :class:`decimal.Decimal`,	|        |
+|                | List["Value"], Dict[QName, "Value"]]				|        |
++----------------+--------------------------------------------------------------+--------+