Switch from TravisCI to Github Actions

This doesn't have full feature parity with Travis in that I'm only
testing the latest stable Rust version. I should *probably* get a bit
more comprehensive in my testing, like the examples give:
https://github.com/actions-rs/example/

However, it's generally fine for my purposes to just tinker with this
codebase when I feel like, and not make substantial efforts to do
anything fancy or bleeding edge.

.github/workflows/ci.yaml

@@ -0,0 +1,21 @@
+name: ci
+
+on:
+  push:
+    branches: [ master ]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Build
+      run: cargo build --verbose
+    - name: Check formatting
+      run: cargo fmt -- --check
+    - name: Run tests
+      run: cargo test --verbose

README.md

@@ -1,4 +1,4 @@
-[![Build Status](https://api.travis-ci.com/DavidCain/stay-the-course.svg?branch=master)](https://travis-ci.com/DavidCain/stay-the-course/)
+[![Build Status](https://github.com/DavidCain/stay-the-course/actions/workflows/ci.yml/badge.svg)](https://github.com/DavidCain/stay-the-course/actions)
 
 
 _This tool is a work in progress, and a first project to learn Rust._