Make it possible to express independence within a layers contract

[seddonym]

It would be nice to express independent layers within a layers contract by putting the layers on one line, like so:

[importlinter:contract:my-layers-contract]
name = My three-tier layers contract (multiple root packages)
type = layers
layers=
    high
    medium_green medium_blue medium_yellow
    low

[flaeppe]

I've actually implemented a version of this in one of the projects I'm working on. With nearly identical config as you're suggesting here.

Let me see if I can port it to a PR draft here, if you want?

[flaeppe]

I pushed #162, if it's of interest. Have a look if you wish

[seddonym]

Thanks for the contribution! Will definitely look at the draft PR when I come to tackle this.

[seddonym]

This is now available as of v1.11, enjoy!