If a document is written with a new path, currently, in the event that
the write fails, the document still gets its path changed. This fixes
it so that the path is not updated unless the write succeeds.
The way that document writes are handled are by submitting them to the
async job pool, which are all executed opportunistically out of order. It
was discovered that this can lead to write inconsistencies when there
are multiple writes to the same file in quick succession.
This seeks to fix this problem by removing document writes from the
general pool of jobs and into its own specialized event. Now when a
user submits a write with one of the write commands, a request is simply
queued up in a new mpsc channel that each Document makes to handle its own
writes. This way, if multiple writes are submitted on the same document,
they are executed in order, while still allowing concurrent writes for
different documents.
