Add file watcher support

[oubiwann]

Use case (only applies to files that are loaded in-memory):

• When enabled (e.g., dev mode), a file that is edited should be re-read and the resource map updated with content/body bytes, accordingly.

Tasks:

• [x] Clean up current resource map
  • [x] Store doc root as absolute path
  • [x] Ensure that path keys are not prefixed with doc root
  • [x] Establish conventions for middleware to use the lmug-state gen_server
  • [x] Store data in a key that matches the middleware name
  • [x] Move all middleware-specific logic currently in lmug-state to lmug-mw-<name>-state
  • [x] Update all current access to use the new state key
• [x] Provide a means of translating between URL path (resource) and file on filesystem (probably absolute path to file)
• [x] Add options for file-watching to the middleware setup (including enabling)
• [x] Enable the use of the 5HT/fs in the repo (rebar dep, app startup, etc.)
• [x] Add listener code (subscriber) that:
  • [x] Receives a filename
  • [x] Does a lookup to resource key
  • [x] Re-processes that file/resource
  • [x] Updates the resource map with the latest content bytes
• [x] Support updates that remove files from the watched directory
• [x] Support updates that add files to the watched directory

Resources:

• https://github.com/5HT/fs

[oubiwann]

I ended up not being able to use 5HT/fs as-is ... had to fork it and make some changes (including adding a new subscribe/2 function). The forked and updated repo is here:

• https://github.com/erlsci/fs

[oubiwann]

Move this one to it's own ticket:

• [ ] Update the middleware config to support exclude patterns

[oubiwann]

Done!