REORG: channel: finally rename the last bi_* / bo_* functions

REORG: channel: finally rename the last bi_* / bo_* functions

For HTTP/2 we'll need some buffer-only equivalent functions to some of
the ones applying to channels and still squatting the bi_* / bo_*
namespace. Since these names have kept being misleading for quite some
time now and are really getting annoying, it's time to rename them. This
commit will use "ci/co" as the prefix (for "channel in", "channel out")
instead of "bi/bo". The following ones were renamed :

  bi_getblk_nc, bi_getline_nc, bi_putblk, bi_putchr,
  bo_getblk, bo_getblk_nc, bo_getline, bo_getline_nc, bo_inject,
  bi_putchk, bi_putstr, bo_getchr, bo_skip, bi_swpbuf