QGIS 2.0 now uses SIP v2 so some QVariant types don't exist anymore
That's the case for QString.

Also added qgismaximumversion in metadata for QGIS2.0 plugin manager
compatibility
Merge pull request #3 from tqhien/master

QGIS 2.0 now uses SIP v2 so some QVariant types don't exist anymore 

Thanks for this work :-)