Conversion to PCL

Converted to a Portable Class Library.  Using PCL Profile78, which is Windows 8, Windows Phone 8 and .NET 4.5

**Please note**
When building the Nuget packages, the folder DLLs should now go into a folder "portable-win+net45+wp80" and not "net40" as before. In other words, your Nuget folder should be 
Nuget\lib\portable-win+net45+wp80

**Also Note**
.NET 4.0 support is completely removed because of the PCL profile we are using.  If .NET 4.0 support is still required we will need to create a separate project for that and will need to included some #IFDEF statements in the source code to do conditional compilation