Create a benchmark project.

[glennawatson]

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Do you want to request a feature or report a bug?
feature

What is the expected behavior?
Lets add a bench marking framework based on BenchmarkDotNet

What is the motivation / use case for changing the behavior?
So that we can get performance differences with new implementations of our code base. Focus more on getting something that performs well for end users.

[glennawatson]

@RLittlesII is going to tackle this one. He's going to focus on classes that have dependencies for ReactiveList due to #1372 and do a initial PR for that, but will tackle later classes separately.