Redis hash and string commands

[jettify]

I have implemented hash commands. Solution for type casting is some what ugly, anyway I need to start from somewhere, so please review. Bit later I will add more method arguments checks, for now I need general idea validation.

[popravich]

Ok, I've looked throught and here is my thoughts.
I'am not really happy with encoder=... parameter:

• first of all its name -- its purpose to decode reponse but it named 'encoder' -- this is confusing.
• second (and major reason why I discorage this) -- I think decoding Redis responses is up to
  end-user of the library.

I aggree that working with raw bytes is not a very good idea, so here is the ticket for thinking on how to deal with it #16.

[jettify]

You are right, my bad.

• ^encoder^ removed
• until response decoding #16 is not resolved, I assume that everything is bytes, and end user is responsible for decoding

[jettify]

I'll decompose this PR to smaller parts.