Can't find how to retrieve the list of all users. #67

Is your feature request related to a problem? Please describe.
The get_users() method only returns the 50 first users.

Describe the solution you'd like
The get_users() method should accept an offset parameter to retrieve next users after the first 50 users has been retrieved.

Additional context
Attached test.py script compare rocketchat_API and rocket-python behavior.
test.py.gz

Here is the script output :

~$ ./test.py 
== rocketchat_API ==
50 users
61 users
== rocket-python ==
50 users
100 users
150 users
200 users
250 users
300 users
350 users
400 users
...                 <- never ends because offset is ignored