Add theme import smart returns

[ben-rogerson]

This PR makes the theme import a little smarter when an array is found.
It'll return different values dependant on the key name.

For example:

theme`fontFamily.mono`;

// ↓ ↓ ↓ ↓ ↓ ↓

"ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, \"Liberation Mono\", \"Courier New\", monospace";

The returned value is a string but in your merged config the value is defined as an array.

Read the tailwind docs for more info.