Add support for stream and buffer protocols.
Stream protocol is abstraction of serial I/O. Buffer protocol is abstraction of random-access I/O. These protocols are defined down to C level, to allow generic, while still efficient algorithms to be coded in C (like, buffered transfer between 2 stream objects, saving/loading of buffer object to/from stream, etc). (Note that CPython define buffer protocol on C level, but apparently not stream protocol).