Develop

This code is ready for review / discussion. I set the version to 1.3.0a1.

Non-backward compatible changes

    Changed the numbering of fields in the MSH segment. This breaks older code.
    Parse all the elements of the message (i.e. down to sub-component). The inclusion of repetitions will break older code.

Others:

    implemented a basic escaping mechanism
    new constant ‘NULL’ which maps to ‘”“’
    new isfile() / splitfile() functions to identify file (FHS/FTS wrapped messages)
    new mechanism to address message parts via a symbolic name

Tests are updated
Docs are updated