PyPy support (#985)

* Run tests on PyPy (#984)

Remove unnecessary `jobs.build.strategy.max_parallel` attribute

* Workaround `symlink() is not implemented for PyPy on Windows`

* Quote conditions in tests workflow file

* Fix quoting in Poetry installation script

* Adjust timeout when testing on pypy

Running the tests with coverage pytest plugin makes some tests run slower than expected

* Try to fix uvloop build errors on macos-latest

* Try to fix uvloop build errors on macos-latest (2)

* Adjust timeout when testing on pypy (2)

* Increase timeout even more

* Try to fix uvloop build errors on macos-latest (3)

* Update tests.yml, revert changes in test files

Add and improve step names
Merge "Lint code" and "Check code-style" steps
Don't install uvloop on macos when running on pypy
Don't run tests with coverage on pypy
Remove test timeout adjustments

* Fix condition

* Update README, add changelog

* Put environment info (`IS_PYPY`, `IS_WINDOWS`) into environment variables

* Fix conditions

README.rst

@@ -61,6 +61,7 @@ Features
 
 - Asynchronous (`asyncio docs <https://docs.python.org/3/library/asyncio.html>`_, :pep:`492`)
 - Has type hints (:pep:`484`) and can be used with `mypy <http://mypy-lang.org/>`_
+- Supports `PyPy <https://www.pypy.org/>`_
 - Supports `Telegram Bot API 5.3 <https://core.telegram.org/bots/api>`_
 - Telegram Bot API integration code was `autogenerated <https://github.com/aiogram/tg-codegen>`_ and can be easily re-generated when API gets updated
 - Updates router (Blueprints)