Simplify usage

[theofidry]

I still find the PHAR-Updater really backbone which leads to way too much boilertemplates for each project. A good example is the difference between PHP-Scoper and Infection self update commands. There is way too much boiler-templates, the usage is not clear enough.

IMO we should provide a Symfony bridge so that adding a self-update command would not be more than registering a command that might need a bit of configuration but not more. If too opinionated for some people, they could always do things their own way instead of using the default command.

It might be worth to check how other projects did it as well and go for a sane default. Even if very big BC breaks, 2.0 should be done right.