descriptors' contains server descriptors.

This is a handy function for simple usage, but if you're reading multiple
descriptor files you might want to consider the
:class:`~stem.descriptor.reader.DescriptorReader`.

Descriptor types include the following, including further minor versions (ie.
if we support 1.1 then we also support everything from 1.0 and most things
from 1.2, but not 2.0)...

========================================= =====
Descriptor Type                           Class
========================================= =====
server-descriptor 1.0                     :class:`~stem.descriptor.server_descriptor.RelayDescriptor`
extra-info 1.0                            :class:`~stem.descriptor.extrainfo_descriptor.RelayExtraInfoDescriptor`
microdescriptor 1.0                       :class:`~stem.descriptor.microdescriptor.Microdescriptor`
directory 1.0                             **unsupported**
network-status-2 1.0                      :class:`~stem.descriptor.router_status_entry.RouterStatusEntryV2` (with a :class:`~stem.descriptor.networkstatus.NetworkStatusDocumentV2`)
dir-key-certificate-3 1.0                 :class:`~stem.descriptor.networkstatus.KeyCertificate`
network-status-consensus-3 1.0            :class:`~stem.descriptor.router_status_entry.RouterStatusEntryV3` (with a :class:`~stem.descriptor.networkstatus.NetworkStatusDocumentV3`)
network-status-vote-3 1.0                 :class:`~stem.descriptor.router_status_entry.RouterStatusEntryV3` (with a :class:`~stem.descriptor.networkstatus.NetworkStatusDocumentV3`)
network-status-microdesc-consensus-3 1.0  :class:`~stem.descriptor.router_status_entry.RouterStatusEntryMicroV3` (with a :class:`~stem.descriptor.networkstatus.NetworkStatusDocumentV3`)
bridge-network-status 1.0                 :class:`~stem.descriptor.router_status_entry.RouterStatusEntryV3` (with a :class:`~stem.descriptor.networkstatus.BridgeNetworkStatusDocument`)
bridge-server-descriptor 1.0              :class:`~stem.descriptor.server_descriptor.BridgeDescriptor`
bridge-extra-info 1.1 or 1.2              :class:`~stem.descriptor.extrainfo_descriptor.BridgeExtraInfoDescriptor`
torperf 1.0                               **unsupported**
bridge-pool-assignment 1.0                **unsupported**
tordnsel 1.0                              :class:`~stem.descriptor.tordnsel.TorDNSEL`
hidden-service-descriptor 1.0             :class:`~stem.descriptor.hidden_service.HiddenServiceDescriptorV2`
========================================= =====

If you're using **python 3** then beware that the open() function defaults to
using text mode. **Binary mode** is strongly suggested because it's both
faster (by my testing by about 33x) and doesn't do universal newline
translation which can make us misparse the document.

::

  my_descriptor_file = open(descriptor_path, 'rb')

:param str,file,tarfile descriptor_file: path or opened file with the descriptor contents
:param str descriptor_type: `descriptor type <https://metrics.torproject.org/collector.html#data-formats>`_, this is guessed if not provided
:param bool validate: checks the validity of the descriptor's content if
  **True**, skips these checks otherwise
:param stem.descriptor.__init__.DocumentHandler document_handler: method in
  which to parse the :class:`~stem.descriptor.networkstatus.NetworkStatusDocument`
:param bool normalize_newlines: converts windows newlines (CRLF), this is the
  default when reading data directories on windows
:param dict kwargs: additional arguments for the descriptor constructor

:returns: iterator for :class:`~stem.descriptor.__init__.Descriptor` instances in the file

:raises:
  * **ValueError** if the contents is malformed and validate is True
  * **TypeError** if we can't match the contents of the file to a descriptor type
  * **IOError** if unable to read from the descriptor_file
Nz