added find_IR.py
replaced a hardcoded max isoform with  a user-defined one as well as  a default value.

added a report of number of excluded genes
first working version
rename find_IR.py to find_RI.py

added test data for find_RI.py
renamed find_IR to find_RI
added test for find_RI.py
added tests for multiple retained introns in a single gene.
removed test_data/RI.test.text
added test data for find_RI_test.py