MEDIUM: buffers: rename a number of buffer management functions

MEDIUM: buffers: rename a number of buffer management functions

The following renaming took place :
1) buffer input functions
  buffer_put_block => bi_putblk
  buffer_put_char => bi_putchr
  buffer_put_string => bi_putstr
  buffer_put_chunk => bi_putchk
  buffer_feed => bi_putstr
  buffer_feed_chunk => bi_putchk
  buffer_cut_tail => bi_erase
  buffer_ignore => bi_fast_delete

2) buffer output functions
  buffer_get_char => bo_getchr
  buffer_get_line => bo_getline
  buffer_get_block => bo_getblk
  buffer_skip => bo_skip
  buffer_write => bo_inject

3) buffer input avail/full functions were introduced :
  bi_avail
  bi_full