Inconsistency in session.start() return values

[dmitrysleptsov]

Hi Thanks for this great library. I noticed some inconsistency in return value for session.start() method. According to docs, it should return session, present, reason. But looking at the code here, here, here and here we can see, that only two values are returned. It makes it harder to debug, because error can appear in different places (in 2nd or 3rd) argument.

I can prepare a PR to fix it if you don't mind.

[bungle]

The 4.0.0 should be using consistently val, err, ... = function()