Provide error messages in retrieve callbacks

v0.0.4

Add network error messages to retrieve methods

Notify upon network connection status change

v0.0.3

Fix build on GCC < 4.9

Callbacks, load all issues and ignore SSL errors

v0.0.2

SSL errors can be ignored correctly now

First test version

First version with capabilities to retrieve, create and update Redmine resources. Create and update is only supported for issues and time entries for now.