SessionManager: Provide default instance?

This is more thinking ahead and depends on #849 but something I want to discuss:

Would be nice if users could do:

from urllib3 import http # or maybe `session` or `default` or something?

r= http.request('GET', whatever)

Two questions:

1. Is it safe to provide a default instance (or magic property) of SessionManager for people to use? Need to consider single-threaded, multi-threaded, and possibly multi-process (this actually might be more safe in a multi-process environment than our current approach where people might accidentally re-use a late-instantiated pool).
2. What should it be named? I like using http in all of the examples like http = PoolManager(), http = ConnectionPool() etc., so http feels natural to me as a default instance you make http requests through, but I’m open to other ideas. Originally, we used to use pool = PoolManager() but I think http is more friendly in practice.

[haikuginger]

I like it! One (completely nonfunctional) thought - maybe have it in the docs as

import urllib3

r = urllib3.request('GET', 'https://www.google.com/')

It’d behave exactly the same way, and people could obviously still do things the from-import way, but it might help create an unconscious association that the state of that particular SessionManager is embedded in urllib3 as a package, rather than in any particular import of it - does that make sense at all?

I definitely do like exposing that static method more than I do exposing a default session with no abstraction; this way, we can even specifically mark the default session as private (_default_session) so that people aren’t tempted to fiddle with it and mess up the state of another urllib3 consumer in the same process.

[sethmlarson]

Going to close this as SessionManager isn’t being developed currently.