Move CI from Travis to GitHub Actions

Author: mitya57

.github/workflows/main.yml

@@ -0,0 +1,21 @@
+name: tests
+on: [push, pull_request]
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python:
+          - '3.9'
+          - '3.10'
+          - '3.11'
+          - '3.12'
+          - '3.13'
+          - pypy3.10
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python }}
+      - run: pip install Markdown
+      - run: python ./test.py

.travis.yml

@@ -1,6 +1,6 @@
-[![Travis CI status](https://api.travis-ci.org/mitya57/python-markdown-math.svg)][Travis]
+[![Build Status](https://github.com/mitya57/python-markdown-math/actions/workflows/tox.yml/badge.svg)][Actions]
 
-[Travis]: https://travis-ci.org/mitya57/python-markdown-math
+[Actions]: https://github.com/mitya57/python-markdown-math/actions
 
 Math extension for Python-Markdown
 ==================================