Add ext- prefix to json data and support call with -ext/vendor/rep

[pierrejoye]

ext-vendor/repo or ext-name is the current format used in composer itself.

Supporting this syntax will allow composer dependencies solver to call pickleweb directly before calling pickle

[pierrejoye]

I will write a full spec about that. It may not be as easy than expected. A lot of codes must change to actually support that. So maybe getting composer/pickle to simply remove the ext- while calling pickleweb would be much easier.