Pure python fallback dependancy for pyahocorasick.

Project Proposal: [Proposal](https://docs.google.com/document/d/14ThtbrNYY6-gWWghhb_r2KvxlNqouf64S0INswXMc4s/edit?usp=sharing)
Parent issue: https://github.com/nexB/scancode-toolkit/issues/3210
Linked PR: https://github.com/nexB/ahocode/pull/1
We plan to create a pure python fallback dependancy for pyahocorasick.
To achieve this, **instead of creating a wrapper**, we plan to **reuse** almost all of the code from [abusix/ahocorapy](https://github.com/abusix/ahocorapy), with minor modification on top of it.