Major modifications

*Calculates time shift and stride for sub-daily selections
*Returns time resolution (in seconds)
*ROxygen-style metadata
Definition of vertical dimension slices
Major modifications

*Relies on java LatLonRect bbox definition
*Returns pointXYindex for indexing the data slice in case of single x/y coordinate selections
Minor changes in function description
Init replaced by .Rprofile
'Done' message when finished
New dependency on 'abind'