Added more requests

- add-comment
- delete-comment
- update-comment
- find-comment
- list-comments
- add-worklog (doesn't quite work)
- list-worklogs
- find-worklog

The add-worklog request is currently broken. The server responds with a
500er error, and I am not sure, whether it's because of a bug in this
library or a bug in the Jira server.