[IMP] Import taxonomies into `methods` root package

[lasley]

Minor improvement, adds import of taxonomies into the root methods package.

Before:

>>> from wordpress_xmlrpc import methods
>>> methods.taxonomies
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'taxonomies'
>>> dir(methods)
['__builtins__', '__doc__', '__file__', '__name__', '__package__', '__path__', 'comments', 'demo', 'media', 'options', 'pages', 'posts', 'users']

After:

>>> from wordpress_xmlrpc import methods
>>> methods.taxonomies
>>> dir(methods)
['__builtins__', '__doc__', '__file__', '__name__', '__package__', '__path__', 'comments', 'demo', 'media', 'options', 'pages', 'posts', 'taxonomies', 'users']