Add tests and GitHub Actions

Replace the Travis tests, which used a separate repo and no longer
ran, with tests in this repo. Each case in test/cases is indented as
a whole and should be unchanged, with optional syntax, fold and tag
checks. The cases are from the previous tests, plus script-setup.vue
for <script setup> keywords and a sync check in oneline.vim.

test/run.sh runs the cases with Vim in a pseudo terminal, as syntax in
Ex mode isn't the same, and Neovim headless.

test/cases/example.vue

@@ -0,0 +1,160 @@
+<template lang="pug">
+  div.set
+    span(id="123")
+</template>
+
+<template>
+  <template></template>
+  <div></div>
+</template>
+
+<template>
+  <p>{{ greeting }}</p>
+</template>
+
+<script>
+export default {
+  data: function () {
+    return {
+      greeting: 'Hello'
+    };
+  },
+};
+</script>
+
+<script lang="ts">
+import Vue from 'vue'
+import { User } from '@/types'
+
+export default Vue.extend({
+  name: 'Home' as string,
+  data() {
+    return {
+      user: {} as User
+    }
+  },
+  computed: {
+    fullName(): string { // Computed Property returns a string
+      return `${this.user.firstName} ${this.user.lastName}`
+    }
+  },
+  mounted(): void { // The mounted hook returns nothing
+    ...
+  }
+})
+</script>
+
+<script lang="coffee">
+# Assignment:
+number   = 42
+opposite = true
+
+# Conditions:
+number = -42 if opposite
+
+# Functions:
+square = (x) -> x * x
+
+# Arrays:
+list = [1, 2, 3, 4, 5]
+
+`
+function hello() {}
+console.log
+a = 123;
+`
+# Objects:
+math =
+  root:   Math.sqrt
+square: square
+cube:   (x) -> x * square x
+
+# Splats:
+race = (winner, runners...) ->
+print winner, runners
+
+# Existence:
+alert "I knew it!" if elvis?
+
+# Array comprehensions:
+cubes = (math.cube num for num in list)
+
+</script>
+
+<style scoped>
+p {
+  font-size: 2em;
+  text-align: center;
+}
+</style>
+
+<style scoped lang="scss">
+$a: 100px;
+
+div {
+  background: white;
+}
+</style>
+
+<style lang="sass">
+$w: 128px;
+
+.bg
+  $w: 128px;
+    background: white;
+  align-items: center;
+
+canvas
+  width: 100vw;
+</style>
+
+<style lang="less">
+@list: 10 12;
+canvas {
+  background: white;
+  width: 100vh;
+}
+</style>
+
+<style lang="stylus">
+@import 'vendor'
+
+body
+  font: 12px Helvetica, Arial, sans-serif
+
+  a.button
+    border-radius: 5px
+</style>
+
+<route>
+{
+  "name": "home",
+  "meta": {
+    "requiresAuth": true
+  }
+}
+</route>
+
+<docs>
+# This is the documentation for component.
+</docs>
+
+<i18n lang="yaml">
+en:
+  hello: "Hello World!"
+ja:
+  hello: "こんにちは、世界！"
+</i18n>
+
+<i18n>
+{
+  "en": {
+    "language": "Language",
+    "hello": "hello, world!"
+  },
+  "ja": {
+    "language": "言語",
+    "hello": "こんにちは、世界！"
+  }
+}
+</i18n>