Python version option (`--python`) for `init` script.

Merge master into develop

# Conflicts:
#	CHANGELOG.md
#	poetry/__version__.py
#	poetry/packages/dependency.py
#	poetry/version/markers.py
#	pyproject.toml
#	tests/packages/test_dependency.py
#	tests/packages/test_main.py

Release 1.0.9

Fix legacy repositories packages being continuously updated

Fix wrong indentation in mixology

Added git ssh example to docs

Added a cli add git ssh dependency example to documentation for easy reference.

# Conflicts:
#	CHANGELOG.md
#	poetry/__version__.py
#	poetry/installation/pip_installer.py
#	poetry/masonry/builders/editable.py
#	pyproject.toml
#	tests/masonry/builders/test_editable.py

Release 1.0.8

# Conflicts:
#	.github/workflows/main.yml
#	.github/workflows/release.yml
#	.pre-commit-config.yaml
#	CHANGELOG.md
#	CONTRIBUTING.md
#	docs/docs/cli.md
#	get-poetry.py
#	make-linux-release.sh
#	poetry.lock
#	poetry/__version__.py
#	poetry/console/commands/export.py
#	poetry/console/commands/self/update.py
#	poetry/installation/pip_installer.py
#	poetry/masonry/api.py
#	poetry/masonry/builders/builder.py
#	poetry/masonry/builders/sdist.py
#	poetry/masonry/utils/package_include.py
#	poetry/masonry/utils/tags.py
#	poetry/packages/__init__.py
#	poetry/packages/directory_dependency.py
#	poetry/packages/file_dependency.py
#	poetry/packages/package.py
#	poetry/packages/url_dependency.py
#	poetry/packages/utils/utils.py
#	poetry/packages/vcs_dependency.py
#	poetry/puzzle/provider.py
#	poetry/repositories/installed_repository.py
#	poetry/repositories/legacy_repository.py
#	poetry/repositories/pypi_repository.py
#	poetry/semver/__init__.py
#	poetry/semver/patterns.py
#	poetry/utils/env.py
#	poetry/utils/helpers.py
#	poetry/utils/inspector.py
#	poetry/vcs/__init__.py
#	poetry/vcs/git.py
#	pyproject.toml
#	tests/conftest.py
#	tests/installation/fixtures/with-directory-dependency-poetry-transitive.test
#	tests/json/test_poetry_schema.py
#	tests/masonry/builders/test_sdist.py
#	tests/masonry/builders/test_wheel.py
#	tests/masonry/test_api.py
#	tests/masonry/utils/test_package_include.py
#	tests/packages/test_main.py
#	tests/packages/test_package.py
#	tests/puzzle/test_solver.py
#	tests/repositories/fixtures/installed/vendor/py3.7/attrs-19.3.0.dist-info/METADATA
#	tests/repositories/test_installed_repository.py
#	tests/repositories/test_legacy_repository.py
#	tests/vcs/test_git.py

Release 1.0.7

Release 1.0.6

* Fix resolution of path, url and VCS dependencies

* Fix editable installation of Poetry packages

doc: fix issue template links in CONTRIBUTING.md

Update shell completion docs for prezto

fix: Gracefully handle read-only sdists

For a package without dependencies in pypi's database, like p4python,
the sdist is required.  The problem is p4python was developed in
perforce where all files are read-only by default and deleting the temp
directory fails.

So we need to use the custom-built temp directory and specially handle
read-only files to be able to use p4python in poetry.

Fixes #520

Bump actions/cache from v1 to v2