Make Parseq portable

Upgrade solution and project files to Visual Studio 2013. This change
should be backward-compatible.
Make Parseq and Parseq.Silverlight projects portable.
Modify some codes to fit the new target framework.
Remove unused files: .user and .pfx files.
Update NuGet package metadata file to support Portable Class Library projects
Merge pull request #10 from takeshik/feature/make-portable

Feature/make portable