File format description for exon_skip.fa, non_exon_skip.fa files
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exon_skip.fa		- contains alternative exons + surrounding introns
non_exon_skip.fa	- contains non-alternative exons + surrounding introns

each sequence consists of a tripple as follows:

>PREV_INTRON 1 chr: 1 strand: + prev_intron_start: 10600786 exon_start: 10601064 exon_end: 10601081 next_intron_start: 10601425
>EXON        1 chr: 1 strand: + prev_intron_start: 10600786 exon_start: 10601064 exon_end: 10601081 next_intron_start: 10601425
>NEXT_INTRON 1 chr: 1 strand: + prev_intron_start: 10600786 exon_start: 10601064 exon_end: 10601081 next_intron_start: 10601425

where PREV_INTRON,EXON,NEXT_INTRON is followed by a sequence ID chromosome number,strand,  and start/stop of intron/exon/intron
