Improve Linear Project Capabilities

[btn0s]

Hello!

I'm looking to work on adding a few linear capabilities and figured an issue is the best place to start. I'd love to start by adding:

• Edit project metadata (name, summary, dates, etc)
• Create / Update / Remove project milestones
• Add attachments to projects
• Edit project overview (description)

If no one is opposed to this I would like to submit a PR myself for these changes.

Cheers!