[Algorithm] Knuth–Morris–Pratt string-searching algorithm

[Rizzen]

https://en.wikipedia.org/wiki/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm

[cathreya]

Should the code be only in C#?

[Rizzen]

Should the code be only in C#?

You are allowed to use any language, in this case, place it in separated folder in the repo root

[Rizzen]

Closed #14