[RFE]: replace pyinotify with watchdog

Description

The use of pyinotify is predicted on the inotify support, which is, largely, a Linux-only thing. The watchdog module would be preferable, because it supports other frameworks, such as BSD's kqueue.

Considered alternatives

Though there exists a wrapper around kqueue/kevent, that provides inotify-like API on BSD systems (indeed, that's used by the FreeBSD port of pyinotify), using a cross-platform module would be both more straightforward and allow using the more efficient file-watching on more operating systems (like Solaris).