Incidents2csv

Hi Matt,

Here is my first pull request. 

I added an incidents2csv script that can be used to generate a list of incidents in CSV format. (An improved version of Michael's initial script.) I then import that in Google Spreadsheet and we use that as the basis of our incidents review call.

Include some docs update and I defined a paginated_get() that encapsulates the PagerDuty pagination logic.

Let me know what you think.