Expose better API for querying events

[lukaszb]

I believe that cq should be framework/tools agnostic, however I caught myself couple of times running from cq.models import Event within my Django based app.

We should be able to query events in a much better manner. To be specific I would love to be able to query events with explicit ordering and filtering after doing simple library import.

Basically, I'd like to achieve something like:

import cq

for event in cq.query_events('User.StartedSession', limit=50):
    print("{} | User {} logged in".format(event.ts, event.data['email']))

Or something like:

print(cq.query_events(ts="3 days")

which should show events from last 3 days.

Signature of cq.query_events

def query_events(*names, limit=100, order_by='-ts', **filters):
    ...

• names are not named arguments. Might be empty of course - in this case all events, regardless of their types, would be returned
• limit results to first 100 by default. If None given, all matching events are returned
• order_by defaults to -ts, meaning events would be ordered by date of creation, descending. Allows to change or disable order.
• filters: For now it would probably suffice to filter by ts param. It should be similar to what is possible with Django ORM: ts=datetime(2017, 3, 24) (exact comparison) or ts__gte=datetime(2017, 3, 24) (all events created after 2017-03-24) or ts="day" (if string given, should be human readable and would be treated as "show me events from last day/week/month" or number of those like "2 weeks". I'd say this is optional, however I'd strongly advice to implement it as it would be mostly used in my opinion).