Added poetry integration.

Description:
* Fixed github actions;
* Removed requirements.txt;
* Fixed CONTRIBUTING.md;
* Fixed black and flake8.

Signed-off-by: Pavel <win10@list.ru>

docs/contributing.md

@@ -22,38 +22,33 @@ It should be quite straight forward to get started and create a Pull Request.
 
 To make contributing as easy and fast as possible, you'll want to run tests and linting locally. 
 
-You'll need to have **python 3.6**, **3.7**, or **3.8**, **virtualenv**, and **git** installed.
+You'll need to have **python 3.6.2**, **3.7**, or **3.8**, **poetry**, and **git** installed.
 
 ```bash
 # 1. clone your fork and cd into the repo directory
 git clone git@github.com:<your username>/ormar.git
 cd ormar
 
-# 2. Set up a virtualenv for running tests
-virtualenv -p `which python3.7` env
-source env/bin/activate
-# (or however you prefer to setup a python environment, 3.6 will work too)
+# 2. Install ormar, dependencies and test dependencies
+poetry install -E dev
 
-# 3. Install ormar, dependencies and test dependencies
-pip install -r requirements.txt
-
-# 4. Checkout a new branch and make your changes
+# 3. Checkout a new branch and make your changes
 git checkout -b my-new-feature-branch
 # make your changes...
 
-# 5. Formatting and linting
+# 4. Formatting and linting
 # ormar uses black for formatting, flake8 for linting and mypy for type hints check
 # run all of the following as all those calls will be run on travis after every push
 black ormar tests
 flake8 ormar
-mypy --config-file mypy.ini ormar tests
+mypy ormar tests
 
-# 6. Run tests
+# 5. Run tests
 # on localhost all tests are run against sglite backend
 # rest of the backends will be checked after push
 pytest -svv --cov=ormar --cov=tests --cov-fail-under=100 --cov-report=term-missing
 
-# 7. Build documentation
+# 6. Build documentation
 mkdocs build
 # if you have changed the documentation make sure it builds successfully
 # you can also use `mkdocs serve` to serve the documentation at localhost:8000