Reconsider target platforms

[GoogleCodeExporter]

We're now supporting a pretty archaic set of platforms - in particular, I don't 
know how to build a Compact Framework 2.0 solution in any Visual Studio release 
later than 2008.

I think we should keep a set of downloads for these old platforms, but then 
consider moving to a system of just building the desktop version and a PCL 
version. (Do we even support the PCL at the moment? That's a more important 
platform moving forward, I believe.)

Thoughts welcome.

Original issue reported on code.google.com by jonathan.skeet on 24 Sep 2013 at 6:11

[GoogleCodeExporter]

Yes, you have PCL support. Your currently configured profile is for .NET 4.0, 
SL 4, WP 7, Windows Store and XBox 360.

Anyone can rebuild for a different profile, for instance, I have rebuilt for 
.NET 4.0, SL 5, WP 8, Windows Store, Xamarin.Android and Xamarin.iOS.

Maybe you could supply two different pre-configured profiles to cover more 
scenarios with your binary distribution.

Original comment by kwac...@gmail.com on 29 Nov 2013 at 4:34