Rearrange transport code

- Core types/functions moved from 'beam' to 'libswarm' top-level
- Helper types/functions moved from 'beam' to 'util'

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
Rename Object to Client

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
Rename Obj() to AsClient()

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
Merge pull request #100 from aanand/port-to-libchan-pt2