Extract the RLP and remove go-ethereum dependency

[devbugging]

Closes: #221

Description

This PR extracts the RLP implementation of the go-etheruem package.

It uses git subtree to include the repository and allow updates with the upstream branch. The contents were modified to only include the RLP implementation and remove all the unnecessary files.

I was trying to use git submodule but I had problems due to the fact that it only referenced a whole subrepo as a commit reference, but that commit wasn't really pushed to the ethereum repo for obvious reasons.

DOD:

• [ ] Implemented
• [ ] Released

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For contributor use:

• [x] Targeted PR against master branch
• [x] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• [x] Code follows the standards mentioned here.
• [x] Updated relevant documentation
• [x] Re-reviewed Files changed in the Github PR explorer
• [x] Added appropriate labels

[nozim]

@sideninja I'm trying to understand what is missing here? I can follow up on missing bits if you don't mind.

[devbugging]

@nozim it's pretty much done, but I wanted to make sure everything was correct but just then didn't have time. I would say making sure this way is the right way.

[nozim]

I think cutting dependency while keeping same functionality is already good for this scope. So should be good to merge :)

[devbugging]

We need to make sure it is updated too