added split_strand.py with a simple split function

added split_graph_strand_test.py with simple tests
renamed split_graph_strand_test.py to split_strand_test.py
added functional code that can split genes with more than 2 exons.
added code that checks and splits fused genes.
fixed a problem that messed up gene and transcript IDs.
added code that return neutral graph if strand is not identified.

edges with score = 0.0 is now included in a final graph.
added shorten_utrs.py
added assign_cds2.py
added a strand to output sequences
added genome argument to split()

removed hard-coded genome sequence DB
removed split_strand_test.py as it obsolete.
added a reference parameter, which is required to predict a strand of a transcript.
added the first working version of find_SE.py
removed the bug that merges transcripts from different genes.

transcripts with an unidentified strand are now ignored

splicing events from a gene are now separated.
added the first version of find_A5SS.py
added the first version of find_A3SS.py
only events with number of isoforms < MAX_ISOFORM are included in the output
scripts now only output events with isoforms < MAX_ISOFORM
replace > with <=
added test data for find_SE.py