Add basic Github Actions workflow

Differences to the travis-ci.org CI:
- No gdb backtraces
- No coveralls support

These can be added back in later

Contributes towards #1141

.github/workflows/ci.yml

@@ -0,0 +1,17 @@
+name: CI
+
+on: [push, pull_request, workflow_dispatch]
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [macos-latest, ubuntu-latest]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Build
+        run: make luvit
+      - name: Test
+        run: make test

README.markdown

@@ -1,6 +1,6 @@
 # Luvit 2.0 - Node.JS for the Lua Inventor
 
-[![Linux Build Status](https://travis-ci.org/luvit/luvit.svg?branch=master)](https://travis-ci.org/luvit/luvit)
+[![Linux Build Status](https://github.com/luvit/luvit/actions/workflows/ci.yml/badge.svg)](https://github.com/luvit/luvit/actions/workflows/ci.yml)
 [![Windows Build status](https://ci.appveyor.com/api/projects/status/72ccr146fm51k7up/branch/master?svg=true)](https://ci.appveyor.com/project/racker-buildbot/luvit/branch/master)
 [![Coverage Status](https://coveralls.io/repos/github/luvit/luvit/badge.svg?branch=master)](https://coveralls.io/github/luvit/luvit?branch=master)
 [![#luvit on Freenode](https://raster.shields.io/badge/Freenode-%23luvit-undefined.png)](https://webchat.freenode.net/?channels=luvit)