Update to Poetry from setup.py

The setup.py-style builds are deprecated. PEP 517 introduced the pyproject.toml
way of packing Python projects. This commit switches to this new mechanism and
uses the Poetry build system. The advantage of this system is that a
Rust-inspired lock file is created to lock down exact dependencies and all but
guarantees that future users will be able to build and use the project.

Further, this commit fixes up CI to use Poetry.

Support for Python 3.6 is dropped since it is no longer supported and the
gherkin-formatter does not want to play nice with 3.6.

Testing against Python 3.10 is added.

Other file changes are reformatting due to new formatter versions.

.github/workflows/transient.yml

@@ -11,39 +11,42 @@ jobs:
       uses: actions/setup-python@v2
       with:
         python-version: 3.8
-    - name: Install python dependencies
+    - name: Install Python dependencies
       run: |
-        python -m pip install --upgrade pip
-        python -m pip install -e '.[dev]'
+        python3 -m pip install --upgrade pip
+        python3 -m pip install poetry
+        poetry install
     - name: Check Format
       run: |
-        make check-format
+        poetry run make check-format
     - name: Check Types
       run: |
-        make check-types
+        poetry run make check-types
 
   UnitTests:
     runs-on: ubuntu-18.04
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9]
+        python-version: [3.7, 3.8, 3.9, "3.10"]
     steps:
     - uses: actions/checkout@v2
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v2
       with:
         python-version: ${{ matrix.python-version }}
-    - name: Install python dependencies
+    - name: Install Python dependencies
       run: |
-        python -m pip install --upgrade pip
-        python -m pip install -e '.[dev]'
+        python3 -m pip install --upgrade pip
+        python3 -m pip install poetry
+        poetry install
     - name: Test with pytest
       run: |
-        make unittest
+        poetry run make unittest
 
-  Ubuntu-2004-Docker:
-    runs-on: ubuntu-18.04
+  Ubuntu-Docker:
+    runs-on: ubuntu-22.04
     strategy:
+      fail-fast: true
       matrix:
         feature:
           - cli
@@ -60,8 +63,9 @@ jobs:
           - ssh_command
           - sshfs
           - sanity
+        docker_ubuntu_version: [20.04, 22.04]
     container:
-      image: ubuntu:20.04
+      image: ubuntu:${{ matrix.docker_ubuntu_version }}
       env:
         DEBIAN_FRONTEND: noninteractive
     steps:
@@ -73,16 +77,16 @@ jobs:
     - name: Install python dependencies
       run: |
         python3 -m pip install --upgrade pip
-        python3 -m pip install -e '.[dev]'
+        python3 -m pip install poetry
+        poetry install
     - name: Run tests
       run: |
-        make test-docker-behave-ci-${{ matrix.feature }}.feature
+        poetry run make test-docker-behave-ci-${{ matrix.feature }}.feature
 
-  Ubuntu-1804-VM:
-    runs-on: ubuntu-18.04
+  Ubuntu-VM:
     strategy:
       matrix:
-        python-version: [3.6, 3.8]
+        python-version: [3.7, "3.10"]
         feature:
           - cli
           - build
@@ -94,6 +98,8 @@ jobs:
           - ssh_command
           - sshfs
           - sanity
+        os: [18.04]
+    runs-on: ubuntu-${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2
     - name: Install package dependencies
@@ -106,8 +112,9 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install python dependencies
       run: |
-        python -m pip install --upgrade pip
-        python -m pip install -e '.[dev]'
+        python3 -m pip install --upgrade pip
+        python3 -m pip install poetry
+        poetry install
     - name: Run tests
       run: |
-        make test-behave-ci-${{ matrix.feature }}.feature
+        poetry run make test-behave-ci-${{ matrix.feature }}.feature