Status output in decoder

• The first port of the decoder function now gives the receipt status (1/0) for each message
• Buffer length used in the input of the decoder function is now user-defined (earlier it corresponded to a single message)

Code reorganization

Some code reorganization for better separating generated artefacts from the original source code.

Basic release

This release provides a function for automatically creating Simulink buses from MAVLink headers, and provides a template for writing the s-functions for encoding and decoding.