Re-brand and re-licence core packages

[Daeraxa]

Related to https://github.com/pulsar-edit/pulsar/pull/171 work that was reverted, commit before the revert was e03eeb0 (#171).

• This rebrands atom -> pulsar in a number of readme files
• Removes licence files where they are the standard MIT licence covered by the repo licence.
• Adapts any licences with additional attribution to new format in repo licence - still present as the attribution needs to be preserved.
• Redirects flight-manual links to relevant pulsar-edit.dev links.

This is very likely to clash with the language rename PR https://github.com/pulsar-edit/pulsar/pull/176 but happy to deal with any clashes if 176 is merged first.