See https://github.com/pypa/warehouse/issues/6345 and https://github.com/pypa/warehouse/pull/6368

* Improve the export command

* Update documentation

Mkdir is breaking when folder is already existing, this allows it not to fail if target exists

* Add `-o` flag for `export` command

The export command now prints to standard output by default.  To store the
output in a file, the new `-o <filename>` argument can be used.

* Fix code style

* Improve usage examples for `export` command

* Add missing import statement to exporter module

* Make Exporter class work w/ IO objects for output

* Fix test suite for `Exporter` utility class

* Refactor configuration code

* Add support for local configuration

* Update documentation

* Add the ability to specify path and git dependencies directly in add

* Add the ability to add git and path dependencies via the init command

* Automatically select latest prereleases if only prereleases are available

* Update documentation for the add command

* Add the ability to add complete dependencies in one go

Co-authored-by: rusty <rusty@spoqa.com>

Some programs (ex. Emacs with auto-virtualenvwrapper package) uses
.venv file to auto-determine the virtualenv of the project. Which is
pretty handy. As well as, it doesn't make sense inside a poetry to
try to set the venv, when it is a file.

* Use subprocess.run() to properly capture return codes.
Fixes #1074

* replaced capture_output flag - only available on 3.7

* Ensure the backported CalledProcessError is imported.

* Fix env tests on windows.

* Format and comment fixes

* Fix encoding for files created for building package (issue #1027)

This is minimal set of modifications, which fixed the problem.

There are still more places, where files are open in text mode
without explicit encoding, thus possibly failing on systems not using
UTF-8 console encoding.

* test_api.py use explicit encoding for files.

* get-poetry.py: fix explicit (utf-8) encoding for files open in text mode

* tests: fix explicit (utf-8) encoding for files open in text mode

* poetry init: use explicit utf-8 for created pyproject.toml

* installed: use explicit utf-8 for text files

* layouts: use explicit utf-8 for open text files

* spdx: explicit utf-8 for open text files

* pypi_repository: explicit utf-8 for open text files

* explicit utf-8 for json

* explicit utf-8 for metadata

* explicit utf-8 for requires.txt

* open files with explicit encoding in py27

* fix creation of poetry.bat on Windows

* Make get-poetry.py compatible to py2/3

* Blacked two files to pass linter test

* remove extranous encoding related comments

* rewert broken move of import related to ansible

* removed extraneous comments about opening files in UTF-8

* rewert ansible.release import (keep order of vars unchanged)

* Revert to original content (as it comes from external project)

* all vendored setup.py files in fixtures reverted back to org

* Typing syntax fixes

* Fix some function signatures that were messing with ellipsis
  for example, `fun(a, ...)` is not valid, but `fun(...)` is

* Dict value types - is that legal? (puzzle/provider.py)

* Ignore assigning instance to classes
  (singletons like Infinity in version/utils.py)

* Add basic mypy config

This configuration has all common settings like:

* strict Optional in functions that returns None

* ignore missing imports - this is usual thing

* Check code that has no typing annotation but uses typed classes/functions

This changes the behavior of version command to show the current version
of the project if no arguments are provided.

This change introduces the use of system keyring to store repository
passwords when one is available. Passwords are added to and removed from
the keyring using the config command.

Resolves: #210