If slug is updated, file should be moved

[Stephen Weiss]

Problem statement

nom should keep the file name in sync with the slug metadata.

Currently, a nom can update the note's slug, which gets the slug out of sync with the file name.

Desired Solution

• a default configuration option keeps file names and slugs in sync
• nom update should check to see if the slug was updated - if it is, and the config setting is on, it should attempt to move the file
• if the new filename is already in use, the whole process should roll back