Add a HiDPI favicon.
minor #696 Add a HiDPI favicon. (whatthejeff)

This PR was merged into the 2.3 branch.

Discussion
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Add a HiDPI favicon.

Difference on my retina display:

![buvjv7biuaa5wwo](https://cloud.githubusercontent.com/assets/306525/3951439/8058ac42-26d6-11e4-89f4-3d69904f7b4c.png)

Commits
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c81a658 Add a HiDPI favicon.
updated VENDORS for 2.5.5
[WIP] Adding a quick note explaining paramters.yml.dist a little
minor #701 [WIP] Adding a quick note explaining paramters.yml.dist a little (weaverryan)

This PR was squashed before being merged into the 2.3 branch (closes #701).

Discussion
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[WIP] Adding a quick note explaining paramters.yml.dist a little

Hi guys!

This is really simple, but a WIP because I also want to add an additional link at the top to symfony/symfony-docs#4174 after it's created.

Thanks!

Commits
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2f58ce7 [WIP] Adding a quick note explaining paramters.yml.dist a little
Merge branch '2.3' into 2.5

* 2.3:
  [WIP] Adding a quick note explaining paramters.yml.dist a little
  Add a HiDPI favicon.
Merge branch '2.5'

* 2.5:
  [WIP] Adding a quick note explaining paramters.yml.dist a little
  updated VENDORS for 2.5.5
  Add a HiDPI favicon.