Enhanced code by means of C# 6

I manually went through each class in the main project and judiciously applied the following features of C# 6:
- Expression-bodied members
- Readonly auto-properties
- String interpolation

We can apply the other new features of C# 6 opportunistically.

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In order to build the solution you will need to use Visual Studio 2015. 

In order to run the tests, you *may* need to install the [NUnit Test Adapter](https://bintray.com/nunit/NUnitAdapter/NUnitAdapter/1.2.0.1/view) and run the tests using the Visual Studio test runner - they all pass :smile: 

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I tried to be judicious but I might impaired readability in some cases due to my keenness to apply the new features. A fresh pair of eyes would be greatly appreciated - I am totally open to constructive criticism.

If you want to hold off from merging this into the main branch for a while, I do not mind one bit - I am happy to have had the opportunity to apply some of the new features. 

I am so thankful for regression tests right about now :beer: