This function disowns the bytes in the buffer and returns
them to the caller. It's useful for freeing the buffer, but
keeping the bytes around without doing a copy.

This function is like ply_buffer_remove_bytes, but it
truncates away the end of the buffer instead of shifting
the contents over the start of the buffer.

This function just reads a chunk of bytes from and fd and adds the bytes to the buffer.

Copy and paste ply-logger into a more general ply-buffer class,
so we have a facility to buffer key strokes and process them as necessary