[docs] Compare function coverage to ethereumjs

[ethereumjs](https://github.com/ethereumjs/ethereumjs-monorepo/tree/master/packages/util) has MANY functions, of which we should make a "checklist" of currently implemented equivalents in `essential-eth`.

A good starting-point would be the function [here](https://github.com/bytesbay/web3-token/blob/main/src/lib/verify/decrypter.ts#L2)

```ts
import {
hashPersonalMessage,
toBuffer,
fromRpcSig,
ecrecover,
publicToAddress,
bufferToHex
} from 'ethereumjs-util';
```

Start with the ethereumjs util package and the referenced src/lib/verify/decrypter.ts import list: hashPersonalMessage, toBuffer, fromRpcSig, ecrecover, publicToAddress, and bufferToHex. Compare these with the functions currently implemented in essential-eth and record the matches in a checklist; the work is done when the relevant ethereumjs functions have been reviewed.

Written by the indexing model from the issue text.