Start using new GitHub support for issue templates

Fix a rare segfault

If pip10 is installed and pyopenssl+cryptography are present in the
environment pip's vendored urllib3 will automatically activate its
pyopenssl adapter. This is by design so users can potentially opt-in to
more up-to-date TLS versions than what are provided by their copy of
Python. However, if a user has these packages & subsequently runs
pip install --ignore-installed cryptography then a segfault will occur
due to overwriting an mmap'd shared object.

This commit introduces 2 issue "types", feature request and bug report.

Ref: https://blog.github.com/2018-05-02-issue-template-improvements/

The flag makes pip prefer an older but valid binary distributions over a newer source distributions.

Fixes #3785.

Fix the capitalization of "GitHub".

enable pip cache in appveyor and travis builds

Add a note to the docs about cosmetic changes in PRs

Revendoring script not to rewrite binascii import

It contains the executables: easy_install, distro, chardetect etc.

It should not be picked as vendored library.

Related to https://github.com/pypa/pip/issues/5347

If there is an import from hamster, while we vendor ham, we should
not rewrite it.

Fixes https://github.com/pypa/pip/issues/5347

Add the ability to short circuit Travis CI builds for docs-only changes

Improve Development docs

Document our deprecation policy, plus a few other process details

* Test that trailing os.sep are ignored while searching PATH
* Simplify paths list creation

Switch to CalVer and set a release cadence

Add a comment to tasks/generate.py regarding Windows shell syntax

Conditionally depend on PyYAML based on Python Version

Remove trailing os.sep to avoid false negatives

Update a pypi.python.org URLs to pypi.org

Update License Year