Add an option to poetry install to install only dev dependencies,
e.g. poetry install --dev-only.

Fixes https://github.com/python-poetry/poetry/issues/2572

Fixes #3577.

This makes `poetry version --short <version>` output only the updated
version number, similarly to `poetry version --short`.

* Remove non-existing --path option
* Add missing options

Co-authored-by: Steph Samson <hello@stephsamson.com>

* Added missing Option in install command description

* Remove python 2.7/3.5 compatibility code

This change removes code, dependencies and tests related to python 2.7
and 3.5 compatibility. The minimum supported runtime python version
for poetry is now 3.6.

* tests: mitigate httpretty urllib incompatibility

Relates-to: #3404

* Fixed the command(deleted the `source` because you don't need `source` in
order to run batch files
* Made code of the table look better, nothing changed in client.

`source`poetry env info --path`/bin/activate`
replaced with:
`source `poetry env info --path`/bin/activate`

Resolves: #477

the built-in function being used does not require comprehension and can work directly with a generator expression

Signed-off-by: Rayan Das <rayandas91@gmail.com>

Signed-off-by: Rayan Das <rayandas91@gmail.com>

Signed-off-by: Rayan Das <rayandas91@gmail.com>

Because `.zprofile` is only run for login shells, it is not used
by graphical terminals. `.zprofile` is also not created by default.

Fixes #2620

Resolves: #3236

\#3236 states that some functions are defined but never used, thus this
PR remove then. While removing them, this also makes sure that there is
no trouble with:
```bash
$ poetry run pytest tests/
$ poetry run pre-commit run --all-files
```
as stated at `CONTRIBUTING.md`.

The functions removed were:

- `poetry/config/config.py`:
  + `_get_validator`

- `poetry/console/commands/config.py`:
  + `_list_setting`
  + `_get_formatted_value`

- `poetry/console/commands/run.py` :
  + `_module`

- `poetry/console/commands/self/update.py :
  + `_bin_path`

- `poetry/mixology/version_solver.py`:
  + `_excludes_single_version`

- `poetry/puzzle/provider.py`:
  + `_formatter_elapsed`

- `poetry/utils/setup_reader.py`:
  + `_is_empty_result`

By removing some of those functions Flack announced that there is no
more need to do some includes, so they were removed too:
- `poetry/mixology/version_solver.py`:
  + `from typing import Any`
  + `from poetry.core.semver import Version`
  + `from poetry.core.semver import VersionRange`
- `poetry/puzzle/provider.py`:
  + `import time`

- ensure tests rely on temporary cache directory
- remove external http call requirement for lock --no-update

Relates-to: #1645

* Add context to caret version constraint documentation

Resolves: #3272

Resolves: #3263

When a project specifies non default sources, PyPI gets added as the
default source. This will prioritise packages available in PyPI when
the package exists in both index. This change ensures that PyPI is
only used as a default when no other sources are provided.

Resolves: #1677 #2564 #3238

Resolves: #3213

Previously, when using locked repository, incorrect dependency instance
was created when a dependency's extra requirement activated a
nested extra. This change ensures that these are correctly
loaded.

As part of this change new lock files write PEP 508 serialised form of
extra dependencies in order to reuse core logic to parse specification
of extra requirement.

Resolves: #3224

When detecting installed packages, this change ensures that packages
with .pth files are not incorrectly marked as editable. A package is
considered editable only if at least one of the paths detected is
not in the environment site.

Resolves: #3077

This change ensures that, When using system environment, poetry falls
back to `userbase` if default location is not writable.

This change improves handling of site-packages under system env, by
gracefully handling fallbacks to user site when required and possible.

Resolves: #3079

This change allows users to disable parallel execution while using the
new installer.

Resolves: #3087

Resolves: #1894

This change correctly reverts pyproject.toml changes for dry runs as 
well as keyboard interrupts.

Resolves: #2933 #318

Mitigates: #3134