add STARTTLS

[thallian]

This adds the possibility to connect to an ldap server with STARTTLS.

I am not quite sure if there is a better way of doing this but I found nothing else that worked.

[marcoh00]

Hi! Thanks for caring about the project and even doing some work to make it better :) !

I see the code can call "bind" multiple times now when using STARTTLS. As I don't know a whole lot about ldap3 myself, did you do that on purpose? Do you know which other implications it can have? If not, it would be super-nice to do a little update to the program flow, so it'll bind only once. I will happily merge it then. If yes, please just say so, I am always willing to learn new things and merge it anyway ;)

Thanks again!

[thallian]

Sorry for the long delay. In the meantime I changed my architecture and no longer use STARTTLS, so I can't really test it now.

Looking at the code now, I'd say it should be possible to call bind only once but I have to test this. Allow me a bit of time to set up my testing environment again, then I can give you a definite answer.