Upgrade to Tailwind CSS v3

[hudon]

Tailwind CSS v3.0 is out, so this issue can track the work (if any) needed for this gem to upgrade to it.

Their upgrade guide is here.

[dixpac]

Currently this is not possible.

Tailwind 3 removed classic mode, JIT is the only mode for Tailwind 3.
 This means that if we build tailwind.css with the npx tailwind build > ./app/assets/stylesheets/tailwind.css" we will get almost nothing, 13KB file size that just resets browser default styles.

[dhh]

Note the incompatibility with 3.0 in the README.

[hudon]

This gem now supports Tailwind 3 in v2 and above thanks to this PR: #96