Benchmarks Introduction

[svengeance]

Fixes #127

This PR uses BenchmarkDotNet to introduce benchmarks for the public API of IAppCache, in addition to a couple "integration" scenarios that tie together what should be common use-cases of the program.

Something I purposefully didn't test is the eviction process - since we currently are tied to .NET's MemoryCache for Cache Entry compaction and eviction, I didn't feel it was necessarily our job to test that. Just my 2c though, and I can add it if you'd like.

Lastly, I wrote the README from a generic owner point of view - please modify it as you see fit to fit your preferred style, particularly the Contributing section.

[jnyrup]

Really impressive work 👍

An idea for future refinements.
Would it be interesting to distinguish the two cases?

• The key already exists in the cache
• The key does not exist in the cache

[svengeance]

Updated benchmarks to incorporate distinctions between cache hits & misses. Notably, there is a ~20% difference in performance between a hit/miss for the Get methods, however the other methods have a negligible difference.

[alastairtree]

This looks great, will try and merge this week.

[svengeance]

@alastairtree Anything else you need on this?

[alastairtree]

No it's awesome, thanks. Just not got round to merging!