Upgrade to C# 6

[ethanmoffat]

C# 6 has some nice language features that aren't present in the current source because it is limited to .Net 4.5 features.

1. Lamba methods/properties, i.e. public int Property => 42;
2. Get-only properties, i.e. public int Property { get; }
3. String interpolation, i.e. $"I am a string with a {someInt} interpolated int!

Solution needs the following:

1. Upgrade projects to latest Visual Studio (2017)
2. Upgrade .Net target version for all projects to .Net 4.6
3. Upgrade package dependencies as appropriate

[ethanmoffat]

Upgrade completed. Any related code cleanup will not be linked to this issue but will be checked in as an individual commit.