api_call is more generic

It now takes a hash of arguments to send to PagerDuty
Pagerduty initializer no longer accepts incident key

This breaks backwards compatibility. We'll have to bump up the version
to 2.0.0
Update version 1.4.1 -> 2.0.0
Extract method to ensure response is success
trigger method now accepts only one argument

namely a hash of attributes to be sent to PagerDuty
Test we can send all attributes to PagerDuty

New in this test:
 - incident_key
 - client
 - client_url
description is optional

for resolve and acknowledge event types
The description is a required attribute

make it a required argument in the trigger event
Ensure we can trigger an event without options
use attribute accessors
correct trigger description usage in specs
Merge pull request #19 from envato/allow_client_parameters

Realign to the PagerDuty event API