DataSet: add guessChunking(PSize, size_t elementSize)
PSize: introduce .data() member to access inner array

This avoids undefined behaviour for &size[0] in the case of size.rank() == 0
PSize: Complete +/- operator family
DataSpace::size() new function to return the size
Charon: new createDataSpace overload with a maxims pointer
DataSet::create: new overload that deduces size from a value
PSize: implement operator == and !=
PSize: Implement operators * and /
PSize: implement dot product member function
DataSet::create: Don't init with DSetCreatePropList::DEFAULT

Because this doesn't create a new PropertyList *based* on the
default, but gives as a handle to the actual default. So afterwards
we would actually be modifying the default list. Doh!
DataSet::create: Actually use the custom creation properties

Earlier we modified the default creation property list, so the code
seemed to work; of course we actually want a new property list
and pass that to the create function.
Merge branch 'master' of github.com:G-Node/pandora into odml

Conflicts:
	include/pandora/DataSet.hpp