Updates and adds some package docs.
It also provides autogenerated README's using https://github.com/jimmyfrasche/autoreadme tool. To use it, make sure it's installed on your system, and every time you update documentation, run go generate to update the README.md file.
Added a lightweight logger wrapper around go-ethereum/log which adds StatusIM prefix to all messages and allows to clearly distinguish between status-go and go-ethereum logs.
Logs under vendor/go-ethereum left unchanged because those pieces of code might undergo huge refactoring in the near term.