* Add a env:info command

* Add env:use command

* Fix tests on Windows

* Fix tests

* Fix tests

* Fix tests for Python 3.5

* Use a hash in virtualenv names dependent on the project’s path

* Add tests for the `env use` command

* Fix tests

* Add a `env list` command

* Fix venvs being recreated when switching minor Python versions

* Add a `env remove` command

* Update CHANGELOG

* Update documentation

* Upgrade Cleo to the new improved version

* Update sonnet script to use sub commands

* Improve show command output:

* Handle file and directory dependencies
* Handle git dev-dependencies
* Only include a package's width for output if it needs updating

* Update git show tests to have an outdated git dependency

`develop` has been deprecated in [this commit][1], `install` will
automatically use development mode.

[1]: 48ed586b

In version 0.12.8, attempting to use an uppercase 'F' to designate build format yields the error: 

[NoSuchOption]
 The "-F" options does not exist.
 build [-f|--format FORMAT]

Switching to lowercase 'f' to match the CLI's current configuration.

When loading installed packages pip freeze can output lines with
``===``, arbitrary equals, qualifiers instead of ``==``. This allows
poetry to parse either.

This fixes #433, based on the suggestion present in the discussion.