First pass at MSH4.1 format revision (#444):

 * All the unsigned long entries are changed to size_t
 * All the entries designating counts which were previsouly encoded as int are also changed to size_t
 * The bounding box for point entities is simply replaced by the 3 coordinates of the point (instead of the six bounding box values)
 * The entityDim and entityTag values are switched in the $Nodes and $Elements sections (for consistency with the ordering used elsewhere)
 * The minimum and the maximum tag of nodes (resp. elements) is added in the header of the $Nodes (resp. $Elements) section, to facilitate the detection of sparse or dense numberings when reading the file
 * The $Periodic section has been changed to always provide the number of values in the affine transform (which can be can be zero

Next step: move node and element tags to size_t.