State policy for inclusion of libraries

[cornelius]

We should make it explicit what the policy is for inclusion of libraries in Inqlude.

We do want to be inclusive, so generally all Qt related libraries are ok. We might want to add a few requirements or maybe classify libraries differently which meet more of them. These requirements could be things like:

• At least one stable release
• No Qt 3 libraries
• Provides a Qt API
• Published API docs