Migrate vs2015 preview

hi @dbolkensteyn 

took a look on how to integrate the diagnostics with the visual studio extension, and few things come up.
1. seems the current diagnostics will not work in VS 2015, that will be the next release of visual studio
2. because of 1, the code no longer compiles and even worse the diagnostics are using now ISyntaxNodeAnalyzer<TSyntaxKind> that have been removed for VS 2015 (if i understand correctly).  see in the rosyling source code commit:
Author:		RoslynTeam <roslynteam@microsoft.com>
Author date:	3 months ago (9/18/2014 10:14:28 AM)
Commit date:	2 months ago (9/25/2014 1:46:15 AM)
Commit hash:	010d4bda7f1ec63097feae86d47652ec398c769b
Children:	c05a13e6c1
Parent(s):	c6eaf4af72

Replace IDiagnosticAnalyzer with DiagnosticAnalyzer, and move to an action-based diagnostic analysis model. (changeset 1337816)

Not sure what wuold be the effort to update the diagnostics, but i can take a look to see if i can import a few.

3. notice that you are placing all diagnostics inside the same exe, can you consider spliting those in different assemblies so that they can be easily integrated into third party tools.

This pull request is just to demonstrate the issue.. 

thanks