FileWatcher should create root_path when it doesn't exist; RepositoryWatcher should make the initial pull only after recheck_pending_remote_events_interval elapses

[alfredbaudisch]

Problem

• RepositoryWatcher pulls content from the remote_repository_url as soon as the application is started.
• FileWatcher also starts listening for changes as soon as the application is started.

This sometimes creates rush conditions between RepositoryWatcher and FileWatcher, which leads to FileWatcher getting stuck, for example #51.

This is mainly because when using content from an external repository, the content root_path folder may still not exist in the server when the application is started, because the folder is created by RepositoryProviders.Git.

This only happens when remote_repository_url is set.

Proposed Solution

1. Upon application start, before FileWatcher starts watching for changes, it should check whether root_path exists, if not, creates it.
2. Validate configuration upon application start: crash if recheck_pending_remote_events_interval < recheck_pending_file_events_interval.
   • Add the validation as the first thing into PardallMarkdown.Application.start/2 or try something like Vapor (although Vapor doesn't support custom validators).
   • Docs should mention that recheck_pending_remote_events_interval must be greater than recheck_pending_file_events_interval.
3. RepositoryWatcher should start watching for changes after the first recheck_pending_remote_events_interval elapses.
   • Currently it starts pooling for changes right away, and uses recheck_pending_remote_events_interval only for subsequent pulls.