Message API Documentation update

[ChristopherBignamini]

Hello, thank you very much for this very useful library. I'm giving it a try and I think there could be a mismatch between the available API (develop branch/1.3.1 tag) and the README documentation: I may be wrong bu the "list" method doesn't seem to exist in messages API. Indeed, in the test suite the "getMessages" method is used instead. Am I missing something?
Thank you again!