Get build working on Mono

[leafgarland]

There were two issues that I could find that prevented this from building with Mono (on OSX):

• The fsproj files were setup to use a local lib/FSharp but this didn't seem to work (doing things like trying to run fsc.exe directly instead of with mono.exe). I Removed lib/FSharp and references in fsproj files.
• The nuget.targets file was out of date and caused problems on Mono. A later version would fix it but since nuget has switched to the new restore workflow it's not needed anymore. So I removed the old nuget restore bits from the fsproj files.

I've tested this on OSX and Windows (cmd line and VS), looks ok.

[panesofglass]

Turns out I only found a way to get Xamarin Studio to load the project. Unfortunately, XS does not load any library references pushed into Choose blocks. I think the targets file is also getting lost, as both XS and xbuild complain of no Clean, Build, or Rebuild targets.

@leafgarland, would you mind taking a look at my fork, where I merged the latest master branch into your PR?

[leafgarland]

@panesofglass Sure. Your merged fork fails to compile on OSX, but bumping the version number in the fsproj files fixes it. See my comments on your merges to the src fsproj and tests fsproj.

I'll take a look at the changes @dsyme suggested.

[panesofglass]

Thanks again! This has been merged!