File watching should handle rename events

[mbostock]

Currently our file watcher only handles change events. This means that a command such as git checkout docs/index.md which generates a rename event is ignored, and then the file watcher becomes detached from the file and no longer reports any changes.

https://github.com/observablehq/cli/blob/0081db4f685ef635df42d0725ec2bbac5e87fa6c/src/preview.ts#L142

[prichey]

@mbostock What is the desired behavior in the event of an actual rename?

E.g. mv docs/javascript.md docs/javascript-foo.md. If at /javascript, would you expect the page to reload and stay at the same URL (which would now 404), or would you expect a redirect to the new URL? The trivial solution would be to emit a reload, though it might be nice to location.assign (or location.replace?) to the new URL

[mbostock]

@prichey I’d start by making the git checkout use case described above function as intended. I’m not sure we need to support pages getting renamed and redirecting.

[mbostock]

Fixed in #64 #67.