Issue 339: allow using stderr instead of stdout

[yevmel]

at the moment instance of Console used by JCommander is initialized in JCommander.getConsole() and can not be changed. this situation results in issue #339

by making JCommander.console configurable developers can decide on what implementation of Console they are going to use.
using JCommander.Builder like this would resolve issue #339 :

JCommander.newBuilder()
    .args(args)
    .console(new DefaultConsole(System.err))
    .build();

[jeremysolarz]

@cbeust can I merge this? Is #339 worth implementing?

[cbeust]

Done, thanks!