Fix static file change detection on Windows.
Fixed windows uses different filepath separator. The filepath.ToSlash
shouldn't be used, because it can cause errors in filepath suffix and prefix
testing since "c:\a" isn't a prefix of "c:/a/b/c".
Avoid locking the files for an extended amount of time. Sublime Text
doesn't like this and shows an error when modifying a file in rapid
succession.
Added batching behavior for page building.

Quite often file watcher gets many changes and each change triggered a
build. One build per second should be sufficient. Also added tracking for
new folders.
Don't shutdown hugo on an empty file.
Allowing empty files (ignored) so you can touch a new file while watching
Example of a multilingual site.