Add package testing to CI (#68)

* Make `build_examples.py` callable from python
* Allow tests to run from outside project directory
* Add invoke tasks
* Add server tests
* Run travis tests against wheel package instead of local code
* Update `badge.write_badge()` to support `pathlib.Path`
* Update `CONTRIBUTING.md`

docker/test/Dockerfile

@@ -0,0 +1,8 @@
+FROM python:3.10.0
+
+WORKDIR /work
+
+RUN apt update && pip install -U pip
+COPY requirements.txt ./
+RUN pip install -r ./requirements.txt
+COPY run_docker_tests.sh ./

docker/test/requirements.txt

@@ -0,0 +1,4 @@
+packaging
+pytest
+pytest-cov
+requests

docker/test/run_docker_tests.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+echo "Running tests..."
+mkdir tmp && cd tmp
+mkdir tests
+pip install /app/dist/anybadge*.whl
+pytest --doctest-modules --cov=anybadge --cov-report html:htmlcov /app/anybadge /app/tests