Update buffers to make use of defrecord.
Update buffers to make use of defrecord.

* created a defrecord for each with-meta type.
* ::buffer becomes Buffer, etc.
* added the new types to our isa heirarchy.

ethancrawford/overtone,brunchboy/overtone,craftybones/overtone,mcanthony/overtone,pje/overtone,la3lma/overtone,Widea/overtone,rosejn/overtone,chunseoklee/overtone