build config: switch from tox to github actions

replace bsddb with berkeleydb

bsddb3 is deprecated

install libdb-dev in github actions

[requirements-test] proper requirements for tests

tests directory, add __init__

library does not support Python 3.6 now (due to bsddb)

This will be fixed on next PR. Here we only fix builds

Revert "replace bsddb with berkeleydb"

This reverts commit 478dd33.

[github workflows] add caching of requirements

.github/workflows/main.yml

@@ -0,0 +1,41 @@
+name: CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: [3.5]
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: libddb
+      run: |
+        sudo apt-get install libdb-dev
+
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Cache pip
+      uses: actions/cache@v2
+      with:
+         path: ~/.cache/pip
+         key: ${{ runner.os}}-pip-${{ hashFiles('tests/requirements-test.txt') }}
+         restore-keys: |
+           ${{  runner.os}}-pip-
+           ${{ runner.os}}-
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install -r tests/requirements-test.txt
+    - name: Test with pytest
+      run: |
+        pytest

tests/requirements-test.txt

@@ -0,0 +1,3 @@
+-r ../requirements.txt
+mock
+pytest