0.4.0

CHANGES:

• Remove Bytebuffer from public api
• Deprecate schedule_bigstring, write_string
• Support reading lines from an input channel
• Use Core_unix.IOVec to represent a view inside the input channel
• Support file descriptors that don't support nonblocking IO
• Remove the read_one_chunk_at_a_time interface from input channel
• Switch to 0.15 series of core and async