Add support for more project metadata

[kylewlacy]

The top-level export const project in a project can currently include the fields name and version (extra fields can be included, but aren't semantically meaningful). We should support some other useful fields too:

• website: Link to official project website
• license: SPDX license specifier

There might be some other fields like repository, issueTracker, authors, etc that might also be worth adding, but website and license are a minimum good starting point as many users are likely going to want to know these details at a glance. Adding these details now will also be helpful if/when the registry has an interface for exploring packages, where listing the license and website details up-front will be helpful

Licensing details can also get complicated, such as ffmpeg builds that can be legally-encumbered and not redistributable depending on what codecs are enabled at build time. We can punt on handling these kinds of edge cases for now, and just say that the license field should be set based on the project's license and source code, and should only be set if it's unambiguous what the resulting license will be for every build