Feature Request: Provide v4-shim.js support

[alexdiliberto]

https://fontawesome.com/how-to-use/upgrading-from-4#v4-shim

Our application allows us to render .hbs content snippets from externally trusted sources. We would like the ability to allow these external users to slowly "opt-in" over time to Font Awesome v5.x, as almost all are currently using the <i "fa"> syntax and in our current Font Awesome v4.x environment using ember-font-awesome, these get properly converted and rendered correctly and everything "just works".

If we could now include the v4-shim on our end after upgrading to v5.x, then everything should just continue to work as expected until users do a proper upgrade.

Let me know if there are any considerations that need to be made there which I haven't yet thought of. Thanks

[robmadole]

This is a pretty good idea. We have some of this work done in fontawesome-svg-core because our quick-n-easy lib uses shims.