Pull in dependencies at build time instead of storing them as source

[gggeek]

In order to make it easier to maintain this package, it would make more sense to not have a copy of all the dependencies stored in the "lib" folder, but instead only pull them in at build time.
The advantage would also be that the tarball gotten from github would be smaller, as it would include 'just' the phar file.

One idea about how to achieve this could be to use a separate composer.json file that declares the required php depenendencies and it used by makephar.php, but is not parsed when the main composer.json of this project is parsed by the top-level project :-)