[MEDIUM] buffers: rework the functions to exchange between SI and buffers

There was no consistency between all the functions used to exchange data
between a buffer and a stream interface. Also, the functions used to send
data to a buffer did not consider the possibility that the buffer was
shutdown for read.

Now the functions are called buffer_{put,get}_{char,block,chunk,string}.

The old buffer_feed* functions have been left available for existing code
but marked deprecated.
3 files changed