fix: highlight at runtime and add todomvc example

[ulivz]

What kind of change does this PR introduce? (check at least one)

• [x] Bugfix
• [x] Feature
• [ ] Code style update
• [ ] Refactor
• [ ] Build-related changes
• [ ] Other, please describe:

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• [ ] When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• [ ] All tests are passing
• [ ] New/updated tests are included

If adding a new feature, the PR's description includes:

• [ ] A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

[codecov-io]

Codecov Report

Merging #2 into master will decrease coverage by 18.05%. The diff coverage is 50%.

@@            Coverage Diff             @@
##           master      #2       +/-   ##
==========================================
- Coverage   95.55%   77.5%   -18.06%     
==========================================
  Files          10       6        -4     
  Lines          45      40        -5     
  Branches        6       6               
==========================================
- Hits           43      31       -12     
- Misses          2       9        +7

Impacted Files	Coverage Δ
lib/index.js	0% <0%> (ø)
lib/ExamplePreviewFileContent.vue	100% <100%> (ø)	:arrow_up:
lib/ExamplePreview.vue	96.42% <66.66%> (ø)	:arrow_up:
lib/ExamplePreviewBarButton.vue	0% <0%> (-100%)	:arrow_down:
lib/icons/brackets.svg
docs/examples/counter/Counter.vue
docs/examples/counter/App.vue
lib/icons/codesandbox.svg
docs/examples/counter/index.js
... and 1 more

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