This change ensures that invalid versions in setup files raises an 
error and gracefully fallsback to PEP 517 builds to discover package
metadata.

Resolves: #2761

The previous VERSION_REGEX string only checks for 'RC', however, the
latest RC submitted to the poetry project is '1.1.0rc1' which fails the
regex test for allowing installation of PREVIEW releases.

fixes: https://github.com/python-poetry/poetry/issues/2977

Release 1.1.0rc1

This change cleans up a few of the fixtures used in the test suite to
be more consistent and also renames ambiguous helper classes.

Resolves: #2576

Resolves: #711

provider: ensure download dest file is a string

Resolves: #98

Before this change, when .venv directory exists  within the project 
root, poetry will use it as the path to the venv regardless whether 
virtualenvs.in-project is set to true or not. This leads to confusion
as described in #1770 and #2756.

With this change poetry will check if virtualenvs.in-project is set to
true if it finds a .venv folder.

This commit also changes the default state of this configuration to be
unset (null), in order to not break any current environments.

Resolves: #1770 #2756

* changelog: fix 1.1.0b4 links

* changelog: add missing change for 1.1.0b3

Resolves: #2931

Bump version to 1.1.0b4

* dep: update identify

* deps: update requests-toolbelt

Resolves: #2939

I also added the `-` argument to `python`, because without it you cannot simply append flags for the script.
Hope this is just the same for powershell, as for bash.

Cf. #898

Fix inconsistencies with release scripts

Python 2 running on Windows, causes thread leaks which
leads console io write errors when using pastel. This
works around the issue by limiting to a single worker
in these environments.

Release 1.1.0b3

Fix and improve handling of extras while resolving dependencies