[Request] Add macro support for intellij

[Daenyth]

Currently intellij isn't able to know the types of the sql macro.

This can be fixed by:

1. Defining an intellij macro expansion/typing extension.
2. Publishing those extensions as a jar with some metadata in the manifest
3. Modifying the META-INF section of skunk's jar to point at those extensions

(I know this is a "won't fix" from Rob, I'm just filing this here for someone else to work on)

[trobert]

I've written an extension: https://github.com/trobert/skunk-intellij

Not sure where to publish it for the 3. Will try to have a look when I have some time.

[Daenyth]

It seems like this has been stable and working for a long time, it would be nice to PR it into the scala plugin itself so it works out of the box