Refactor: cbuf naming

[gparmer]

cbufs are currently named too awkwardly. In the future, persistent cbufs are going to be much more common (for programmers to use) than transient memory cbufs. However, the naming scheme makes it more difficult to use them.

Suggested change:

• cbuf_* -> scbuf_* for scoped cbufs which is a more relate-able name for transient memory cbufs.
• cbufp_* -> cbuf_* so now the namespace for persistent cbufs becomes easier to use.