chore::> Derive public key from private key using crypto package

[PsychoPunkSage]

Addresses #590 pointer 4

[PsychoPunkSage]

@thiagodeev
were you talking about something like this??

[thiagodeev]

Yes @PsychoPunkSage! That's exactly what I had in mind.
But now, I believe we can do better. Sorry about that, but I'm going to ask you to take another approach.

[PsychoPunkSage]

Hmm,
Okay... I thought about this approach when I started working on the issue.. but it was not that appealing to me to create all the fn again. Instead I was thinking to modify the existing func and check whether user is passing a pub_key or not.. if not then do the required computation...

This approach will surely make things clean but don't you think it will be redundant??
What do you think @thiagodeev ??

[thiagodeev]

This was also my first intention on this feature, but I realized that the MemKeyStore is not a simple privateKey pointer, is literally a "key store", that can store multiple keys and have multiple use cases. If we change it directly, users who are using this feature could be in trouble.
Being so, creating a new abstraction specific to our intention (a Signer), having a new or existing MemKeyStore linked (covering both use cases) and specific methods to it it's a valid approach IMO. What do you think?

[PsychoPunkSage]

Mmmm,
Yeah I think for now we can do that, well, it can always be modified in future by any new contributor.
So, I will separate it...

[PsychoPunkSage]

@thiagodeev have a look

[thiagodeev]

Great job @PsychoPunkSage!
I'll ask one general thing: please put descriptions in the code (package, functions, and methods).
Besides that, I left a few comments

[thiagodeev]

Hey @PsychoPunkSage, left some comments.
An observation: you need to put golang doc code comments

[PsychoPunkSage]

Hi @thiagodeev
Did required changes. Please have a look whenever you find time.

[thiagodeev]

Hey @PsychoPunkSage, left a few comments, otherwise looks good!

[PsychoPunkSage]

@thiagodeev
Did you find time to review the PR?