Support .NET Core (was: Support Mono 5)

[markfinal]

http://www.mono-project.com/docs/about-mono/releases/5.0.0/

In particular

• note the change from mcs to csc, although that should not change the internal compiler invocation in code (but may be able to remove some of the IsRunningMono conditionals)
• change from .mdb to .pdb, which will simplify the debug symbol code in Core
• support C# 7

C#7 will allow things like:

• auto-property initializers - for Settings classes (from C#6)
• tuples (better than System.Tuple)

An upgrade to the .csprojs will also be required, with a newer VisualStudio required than 2013.

This may suggest either a v1.2.0 or v2.0.0 version number for BAM.

[markfinal]

C# 6 also has string interpolation. C# 6 also has null conditional operators. C# 6 also has nameof expressions. C# 7 has throw expressions.

Other references: https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-6 https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-7

Note that Xamarin Studio in OSX does not currently support C# 7 (build 6.3). Perhaps need to wait for build 7?