Prevent error when using proxies after picking an Adapter
Fixed pickle support for requests.adapters.HTTPAdapter by adding
'proxy_manager' when unpickling.
Updated AUTHORS.
Move comment to the right place
use adapter pool size for proxies
Add more interlinks between the documentation

Also fixes up tense in a few cases, and adds the `intersphinx` extension so we
can link to the urllib3 documentation when it is called out.
Don't let proxy_bypass bring you down.
get_netrc_auth: handle os.path.expanduser failure

os.path.expanduser can raise a KeyError when $HOME is not set and the
POSIX getpwuid() call fails, which can happen when running under a UID
which is not in /etc/passwd or when the password file cannot be read.

The upstream bug report http://bugs.python.org/issue20164 is unlikely to
be backported to Python 2.x even if fixed so this change handles
KeyError by skipping netrc authentication.

Closes #1846
get_netrc_auth: code cleanup

* Stop iterating as soon as we find a netrc file
* More obvious return None
Merge pull request #1831 from kevinburke/interlinks

Add more interlinks between the documentation
Merge pull request #1827 from pepijndevos/master

Use adapter pool size for proxies
Merge pull request #1845 from Lukasa/proxy_bypass

Resolve proxy_bypass problems.
Merge branch 'master' into fix-pickling-adapters

Conflicts:
	AUTHORS.rst
Merge pull request #1846 from acdha/paranoid-get_netrc_auth

get_netrc_auth should handle os.path.expanduser failing