v0.4.0

• Improve parser error handling so that the user gets the byte position
  where parsing failed instead of the number of bytes remaining
• Expand public API to expose more low level deserialization objects.
• Use an Rc<...> to hold definition messages to avoid unnecessary copying.
• Provide an interface that allows a continuous stream of data in addition
  to batch processing (see examples/streaming.rs).
• Implement CRC validation of both the header and data sections.
• Bump packaged FIT SDK version to 21.47.00