stomp.py version changes

[IgnoredAmbience]

As of stomp.py version 5, the connection.start() function has been removed. The use of the function in this code should either be removed, or a compatible major version of the stomp.py version specified.

[poggs]

Are you able to submit a PR?

[IgnoredAmbience]

Which approach would you prefer? I note there's no dependency versioning given in the repo at present, which leaves open the potential for similar regressions in future.

[poggs]

A PR which locks the dependency to the version that the code works with would be the simplest thing to start with - and a PR which uses the latest version with code changes, if you have time, please. But unless there's anything fundamentally better or fixed in the version that deprecates the start() method, the former is a good use of everyone's time

[IgnoredAmbience]

Version 5 of the library removes python 2 support, which might be a step too far for some. PR just adds the version requirement to the pip install line, as I'm still unsure what the preferred python dependency solution is, and adding one to this repo is too much for me at present.