Ask for use-cases in Feature Request Issues

Speeds up the end-to-end running time for Travis tests.

* Adds a new jobs to test_install* separately (using -k "[not] test_install")
* More generic cache ignore
* Move slower Python 3.5 tests before 3.4
* Factor tox envs

When pip was not installed by pip, don't show the upgrade warning

Merge pull request #5339 from jzafran/remove-password-from-stdout

Merge pull request #5286 from benoit-pierre/improve_pep518_build_requirements_handling

Fixes https://github.com/pypa/pip/issues/5346

Suppress warnings about out-of-PATH script installs.

- remove unused `BuildEnvironment` parameter: `no_clean`
- move helper to install build requirement to the `BuildEnvironment` class
- simplify a little the 2 different code paths (with and without build isolation)

Offload more work to the underlying pip command used to install the
build requirements, so there's no need to duplicate code to handle
environment markers/extras. This is done by setting the correct options
from the finder passed in argument to `_install_build_reqs`.

- avoid hitting the index: use `common_wheels`/`script.pip_install_local`
- use `script.pip(..., use_module=True)` to simplify some tests
- improve `test_pep518_uses_build_env` parametrization
- simplify `test_pep518_with_user_pip`: we only need to check build
  requirements can be installed, so no need for testing with both
  `install` and `wheel` command
- fix `test_pip_wheel_with_pep518_build_reqs_no_isolation`: building
  pep518-3.0 without isolation should fail if the build requirements
  are not installed.

- change module name to prevent conflicts with other distributions
- add a `__version__` field for version checks

Keep only one selfcheck.json file

Drop support for Python 3.3

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".