Misc and minor fixes

[lucab]

This is a pile of really small/cosmetic fixes I collected in the last few days. A brief summary of changes:

• constify port numbers as per IANA registry
• synchronize codegen as per my latest PR, to avoid emitting code using unstable features
• add an interactive example; I use this a lot to quickly try stuff, so it may be useful having it here
• update Readme and Cargo manifest with some more details
• tweak Makefile to always execute targets

[Antti]

LGTM.

Thank you!