A new function, Reader::ReadSelectedTags(const set<Tag>&)

Note: this feature request replaces http://sourceforge.net/tracker/?func=detail&aid=2915615&group_id=137895&atid=739587 - [Feature Request] Reader::ReadSelectedTags(const set<Tag>&) - ID: 2915615]

A member function added to gdcm::Reader, to read the values of a set of selected tags in an efficient way.

Proposed signature:
bool gdcm::Reader::ReadSelectedTags(const std::set<Tag>&);

Use case:
////////////////////////////////////////////////
std::set<Tag> selectedTags;
selectedTags.insert( Tag(0x0010,0x0010) );
selectedTags.insert( Tag(0x0028,0x0008) );

if ( reader.ReadSelectedTags(selectedTags) )
{
const gdcm::File& file = reader.GetFile();
const gdcm::DataSet& dataSet = file.GetDataSet();
// Etcetera...
}
////////////////////////////////////////////////

Mathieu already gave me some hints on how to implement such a member function:

1. Read Tag,
2. If tag is in SelectedTagSet, then read Value
3. If not in SelectedTagSet, Skip the Value (do the seekg of ValueLength)
4. If Tag is greater or equal to SelectedTagSet.end() - 1, stops

I think such a function could be very helpful to us at LKEB (www.lkeb.nl).