Add Onivim 2: tiered license pricing + dual license

[nayafia]

Onimvim 2 is a pre-alpha project running a bunch of interesting experiments:

• Free for non-commercial and educational use
• Commercial license is pay-what-you-want, with the minimum pre-order price increasing as they get closer to shipping an MVP
• Anyone who financially sponsors the project (via BountySource, Patreon, PayPal, or OpenCollective) gets a free lifetime license
• Commits are dual-licensed with MIT after 18 months from commit's date to master