Update Yumi_17_01_2014.py

The goal of this script is to generate a new exome file that contains - in the header - the size of the exon itself. That's all. The only problem is that this requires to open the whole file first, which can be huge. That's why I started developing a slightly different code in the beginning of the file, which does not require the big exome file to be read by the read() function. This is now commented out, but should work as well so do not discard.