Cleanup comments.
Removing compiler warning.
Improving IOStream and IOStream::Device.

1. Number conversion base is now an enum for stronger data typing.
2. Added a peekchar() method.
Fixed missing peekchar() for IOStream::Filter.
Ripple effect from IOStream changes.
Improving VWI support for reliable communication in extended mode.

1. Add get_msg_nr() and set_msg_nr() to access message sequence number.
2. Updated VWI example sketches; CosaVWIclient/server with extended mode
retransmission of messages.