• Add channel method "read2".
  
• Do not retry read operations when "libssh2_channel_read_ex"
  returns 0 (bug report by Ferenc Erki).
  
• Fix definitions for LIBSSH2_ERROR_NONE,
  LIBSSH2_SESSION_BLOCK_INBOUND and
  LIBSSH2_SESSION_BLOCK_OUTBOUND.
  
• Scale timeout values passed between IO::Socket::* (using
  seconds) and libssh2 (using miliseconds).
  
• Several documentation improvements.