Feat: Mean

[raphaelDkhn]

Implement Mean operator.

[0xfulanito]

Hey Guys, Can i take this one?

[thelordgiveth]

@0xfulanito are you still working on this?--let me know if you want assistance. You can reply here or @ me on telegram thelord_giveth or the orion discord channel thelordgiv.eth

I would rather use self.mean to complete #259 (right now I have mean in local scope for mvn operator function that would not be ideal to commit).

[0xfulanito]

Hey @thelordgiveth! I appreciate your offer of assistance. I'm actively working on it and plan to have it resolved in the next few days.