Added client support of tnx_id field

[Mikhail Kashkin (xen)]

Hi,
I added support to python client library for tnx_id field which is described as canonical field, but wasn't implemented in client library.

Also, I fixed some documentation indentation issues.

[Fred Blundun (fblundun)]

Hi Mikhail Kashkin (@xen) ,

The Python Tracker used to support the txn_id field. It was a random 6-digit number attached to each event, used for deduplication. You can see the implementation in the first version of the Python Tracker here.

We decided that with only 6 digits, the risk of two events having the same txn_id was still too high. For this reason, we have deprecated this field and we are replacing it with an "event ID" in all our trackers. The event ID is a version 4 UUID, making collisions much less likely. Here is where we add it in the latest Python Tracker version.

I have altered our documentation to make it clear that the txn_id field is deprecated - sorry for the confusion!

[Mikhail Kashkin (xen)]

Well, this makes things little more different for us. Since we plan to use this param as identifier of "active window session id" along with network user id. We will stick with event_id for now. Thank you for clarification.

[Alexander Dean (alexanderdean)]

Closing this PR...

[Mikhail Kashkin (xen)]

Sure.