Added JIRA._fetch_pages function and used it in all functions using pagination and extended ResultList class.
Added JIRA._fetch_pages function and used it in all functions using pagination and extended ResultList class.

Thanks to that, for all these functions items may be fetched in batches.
Fixed some issues found:
- JIRA.search_issues function was throwing an exception on python 3.x because of basestring type used.
- 'total' key is optional in paginated response, but was always expected.
- some parameters in few functions were not documented

pycontribs/jira,dwmarshall/pycontribs-jira,stevencarey/jira,stevencarey/jira,pycontribs/jira,dwmarshall/pycontribs-jira