Ref and close #441
This should also close #767

Summary

This PR prevents {docsify-ignore} and {docsify-ignore-all} to be rendered inside other markdown engines like on Github.

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

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• Repo settings
• Other, please describe:

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

• Yes
• 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)

You have tested in the following browsers: (Providing a detailed version will be better.)

• Chrome
• Firefox
• Safari
• Edge
• IE

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

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Tests

$ mocha ./test/**/*.test.js


  router/history/base
    ✓ toURL without relative path
    relativePath true
      ✓ toURL
      ✓ toURL with double dot
      ✓ toURL child path
      ✓ toURL absolute path

  Docsify public API
    ✓ global APIs are available (183ms)
    Docsify config function
      ✓ allows $docsify to be a function (201ms)
      ✓ provides the hooks and vm API to plugins

  render
    ✓ important content (tips)
    lists
      ✓ as unordered task list
      ✓ as ordered task list
      ✓ normal unordered
      ✓ unordered with custom start
      ✓ nested
    image
      ✓ regular
      ✓ class
      ✓ id
      ✓ no-zoom
      size
        ✓ width and height
        ✓ width
    heading
      ✓ h1
      ✓ h2
      ✓ h3
      ✓ h4
      ✓ h5
      ✓ h6
    link
      ✓ regular
      ✓ linkrel
      ✓ disabled
      ✓ target
      ✓ class
      ✓ id

  router/util
    ✓ resolvePath
    ✓ resolvePath with dot
    ✓ resolvePath with two dots


  35 passing (1s)