Patch for v1 installations

[jhildenbiddle]

• Recommend version-specific CDN URL over latest
• Add placeholder index.js in v1 location with console message indicating an update is available. This will prevent old v1 installations from breaking.

[jhildenbiddle]

Hi again, @jperasmus!

Thought I'd make offer two quick updates that may save some frustration.

• The README update is self-explanatory. This comment reminded me that we should be recommended a version-specific CDN URL to avoid potential issues with future releases.

• The index.js in the root is there as a patch for v1 installs. The call to v1 window.DocsifyCopyCodePlugin.init() is breaking productions sites, so this file provides a placeholder method that prevents the JS error and outputs an update message in the console:

  [Update] docsify-copy-code has been updated. Please see new installation instructions at https://github.com/jperasmus/docsify-copy-code.

  After they update the URL, the other [Deprecation] message will appear in the console if they forgot to remove the v1 stylesheet and init() call in place.

  [Deprecation] Link to external docsify-copy-code stylesheet is no longer necessary.

  [Deprecation] Manually initializing docsify-copy-code using window.DocsifyCopyCodePlugin.init() is no longer necessary.

In hindsight, I wish I had done this in the initial PR. It feels a little weird to have an index.js in the root of an NPM module that is just a patch for older installs, but I don't know of a better way to work around the v2 breaking changes.

Thanks, and apologies for any headaches the breaking change may have caused. 🙄

[jperasmus]

Thanks for the changes, this should alleviate some of the pains we've seen. I don't mind the school of hard knocks - learning from the experience 🤓