Switch to GlobalAssemblyInfo.cs for AssemblyVersion.

All projects under src with a Properties\AssemblyInfo.cs file reference
now reference a common GlobalAssemblyInfo.cs file under src, which
specifies the AssemblyVersion attribute value.
Added GlobalAssemblyInfo.cs itself.
Merge pull request #220 from medianick/master

Switched to GlobalAssemblyInfo.cs for AssemblyVersion attributes.