This PR exposes when using the the `DEBUG` environment variable. This
follows the `DEBUG` conventions where:
- `DEBUG=1`
- `DEBUG=true`
- `DEBUG=*`
- `DEBUG=tailwindcss`
Will enable the debug information, but when using:
- `DEBUG=0`
- `DEBUG=false`
- `DEBUG=-tailwindcss`
It will not.
This currently only exposes some timings related to:
1. Scanning for candidates
2. Building the CSS
3. Optimizing the CSS
We can implement a more advanced version of this where we also expose
more fine grained information such as the files we scanned, the amount
of candidates we found and so on. But I believe that this will be enough
to start triaging performance related issues.
