This is a simple wrapper around posix_spawn() that will help us simplify
a bunch of very verbose posix_spawn() invocations.
This first version only supports the simplest case: executing an
executable without passing arguments or doing anything fancy. More
features can be added to cover more cases. :^)
This commit removes the only 3rd party library (and its usages)
in serenity: puff, which is used for deflate decompression. and
replaces it with the existing original serenity implementation
in LibCompress. :^)
This wrapper abstracts the watch_file setup and file handling, and
allows using the watch_file events as part of the event loop via the
Core::Notifier class.
Also renames the existing DirectoryWatcher class to BlockingFileWatcher,
and adds support for the Modified mode in this class.
