[DX] Cookbook Article for Upgrading Symfony

[weaverryan]

Upgrading Symfony is easy, but I'm not sure everyone realizes this.

http://symfony.com/blog/upgrading-your-symfony-projects-the-easy-way

I propose a quick (because it's easy!) cookbook article about upgrading Symfony:

A) How to upgrade a patch release e.g. 2.5.1 to 2.5.2 (e.g. composer update symfony/symfony).

B) How to upgrade a minor release e.g. 2.5.1 to 2.6.0

C) Details on how to handle dependency issues - i.e. if you try to upgrade to a new version of Symfony, but some other dependency you have is tied to the older version.

D) Other changes you'll need to make - i.e. check the UPGRADE file.... but really, nothing needs to be changed between versions.

[javiereguiluz]

Upgrading the Symfony version is really easy ... but maintaining a fully working application after an upgrade it's another story. To be more precise, was another story when new Symfony versions included lots of BC breaks. Maybe that's the origin of the misconception that makes some developers think that upgrading Symfony is still difficult.

[wouterj]

@javiereguiluz sometimes, there are still changes in the SE that you want to include in your SE. What about also publishing a patch with all changes when bumping the minor version?

[Nicofuma]

By the way, a cookbook entry for upgrading Symfony from 2.3 to 2.4+ could be useful.

[carlos-granados]

Really love this. I never know how to upgrade

[weaverryan]

See #4611!

[weaverryan]

Done! @javiereguiluz we could include a link to the new document on release blog posts ;).