Separate example versions by branch

[xorinzor]

Currently, some examples (like the MVC bookstore) have been updated to 7.0.
The issue is that the documentation for 6.0 (and probably other versions too) all point to the master branch.

This will cause a lot of confusion if people don't pick up on this and attempt to use the example for the wrong version.

Please separate new major versions by branch and update the documentation accordingly to preserve these versions.