move dtype property up to Data object
add astype method on Data objects, add casting options to pack and Data stats methods
minor spelling fixes on README
Merge remote-tracking branch 'upstream/master'
Fix error message
Merge pull request #44 from industrial-sloth/master

Data casting methods
Tutorial updates and fixes
Provide dims as dimensions object using fromTuple
Cast index list as array before flattening
Updated tutorial
automatically cast tuple dims parameters to Dimensions in Images and Series