Snapshot mode

[aleclarson]

When the snapshotPath option is provided, Filespy will pass it to @parcel/watcher's getEventsSince function to see if any files changed since the last time Filespy was given that same snapshot path.

If the snapshotPath exists, the initial crawl will not emit create events. But if the snapshotPath does not exist, Filespy emits create events normally.

When Filespy is closed, it will save the snapshotPath using @parcel/watcher's writeSnapshot function.

See the (outdated) snapshot branch for a proof of concept.

There are 2 blockers to this:

• https://github.com/parcel-bundler/watcher/issues/51
• https://github.com/parcel-bundler/watcher/issues/52