Added a function to produce a GTF-formated list of fields

This can be printed using the csv module. Printing it to STDOUT is a bit tricky because
the string join function doesn't work on the numeric values
This script has been rewritten in python.

The original perl version is still in the Documents/Perl folder
Identical function to the Blast2GTF except that it is written in Python. It also writes the output to a file