We'd like to have a stable location for documentation. The
destination will be https://pythonpaste.readthedocs.io

This change also tries to make sure that there are sufficient
warnings throughout about the status of Paste.

cd/travis ci

We need to use xenial as the dist to get python3.7 working
according to https://github.com/travis-ci/travis-ci/issues/9815

This uses the matrix style for engaging with tox and tests
py27, 35, 36, 37 and pypy.

Python 3 fixes

In Python3, the iterator protocol uses a method named __next__(), not
next(). (For compatibility with Python 2.6, we still need to support
both though.) Ensure all iterator objects support the Python3 protocol.

Signed-off-by: Zane Bitter <zbitter@redhat.com>

This will cause a runtime error in Python 3.7, due to PEP479.

Signed-off-by: Zane Bitter <zbitter@redhat.com>

We can clean it up better as required.

pytest exposes many warnings, some but not all of which are cleaned
up here. The main switch is to use html.escape instead of cgi.escape.
This inspired the addition of 'future' to requirements.

The remaining warnings are related to pytest deprecations or over-eager
test discovery.

It is perhaps ironic that the switch to pytest is to avoid nose being
mostly dead, and now we are using features in pytest that pytest wants
to make dead. These are left for later cleanups, which means that
running the tests is noisy.

Switch from nose to pytest