Using the 2019 Advent of Code as an excuse to learn some C# and XUnit.

I'm using this as an oppertunity to start learning some C#, this should sit quite nicely alongside powershell for situations where I need higher performance.

This isn't pretty, and won't stand up to scrutiny, but is keeping me entertained when I have some free time.

• IntcodeVM is overcomplicated (but works).
• Test coverage is poor (I'm using the tests to build up the solutions and guard against regressions when I refactor).
• I have a lot to learn with C#!