Minor update to tests, added docstrings

Requested by @sigmavirus24.
Merge pull request #1341 from cdunklau/docstring_test_1329

Minor update to tests, added docstrings
Fixed example in authentication docs
Issue #749: Add optional SNI support for python2.

SNI support will be enabled for python2 if ndg-httpsclient and pyopenssl are available.
Merge pull request #1347 from hobarrera/master

Issue #749: Add optional SNI support for python2.
Adding link to documentation in README.rst

Just adding a link to the documentation at python-requests.org
Merge pull request #1342 from mexicat/master

Fixed example in authentication docs
Merge pull request #1352 from nicoddemus/docs-link-on-readme

Adding link to documentation in README.rst
Prevent a KeyError when there's no link headers
Merge pull request #1355 from sigmavirus24/fix_links

Prevent a KeyError when there's no link headers
Adding an argument to the adapter for passing a block argument to the connection pool.

This allows for blocking when using threading to prevent the pool from creating more connections that the max-size allows.

Specifically was seeing the following errors without the block=True:

    WARNING:requests.packages.urllib3.connectionpool:HttpConnectionPool is full, discarding connection: www.example.com
Moving the order of the arguments in the init to not interfere with existing usage.
Fixing the call to init_poolmanagers to correctly unpickle the adapter.
Adding the _pool_bloc to the list of attrs.
Fixes #1320: transport adapters stored in ordered form
Merge pull request #1327 from ambv/adapter_order

Fixes #1320: transport adapters stored in ordered form
Always percent-encode location headers.
Fix for #1362.

`PreparedRequest.prepare_url` incorrectly applied IDNA encoding to the
URLs entire `netloc`.  It should only be encoding the hostname portion
of the URL.  IDNA encoding was limiting the user info, host, and port
segments to be a maximum of 63 characters which causes problems for
all by the most trivial user + password combinations.

- Replaced usage of `urlparse` in `PreparedRequest.prepare_url` with
  `urllib3` equivalent.
- Modified IDNA encoding section so that it only encodes the host
  portion of the URL.
Merge pull request #1363 from dave-shawley/master

Fix for #1362
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