[Feature request] Add an outdated command

[cedx]

Nowadays, most package managers (composer, npm, pub, ...) include an outdated command that displays the packages of the current project which are outdated.

It would be very useful to have the same kind of functionality with haxelib since manually tracking changes in dependencies is very time consuming.
Of course, this command would only apply to packages installed from the Haxelib registry.

[TheDrawingCoder-Gamer]

I'll make an attempt to add that command.
As an outline, what I'll need to do is

1. If no args
   1. Get all libraries in a project (perhaps we can add a "recursive" switch that also applies to meta-dependencies, like npm's --all switch)
   2. For each lib, query the haxelib server for info on a package and find the current version from the installed haxelib json
   3. Compare versions. If Installed Version < Server Version
   4. Print info from this result.
      If there is an arg, do this process only on it.