upgrade tiffsplit to handle more than 2^16 pages

I am new to the library and I wanted to upgrade tiffsplit so it can handle the extraction of more than 2^16 pages. For this, I changed the naming scheme in tiffsplit tool to use 7 digits (starting from 0000001.tif ) and also changed the tiff header addresses to uint32 bit.

I cannot be sure I've done this in the most efficient or correct way as I am new to the library, I know however that these changes will be useful to others who need to split large microscopy/imaging tiff files that these days can easily exceed the 2^16 tiff limit