Proposal: PSD support

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of ImageSharp
• I have verified if the problem exist in both DEBUG and RELEASE mode
• I have searched open and closed issues to ensure it has not already been reported

Description

If at some point there's interest in supporting Adobe PSD, in the past I've used this library: http://psdplugin.codeplex.com/

It's a full featured, pure .Net PSD library. It is the current Paint.Dot.Net plugin to load/save PSD, but the core of the library is stand alone and has no dependencies with Paint.Dot.Net

I used it in the past and it's quite complete and safe to use.