add read trimming script
add read trimming script

- uses cutadapt to trim low quality bases from 3' end
- remove no more than 20 bases (min read length 80)
- short reads loose read specificity (map to many places)
- toss reads if shorter than 80 bp
- because cutadapt designed around adaptor trimming, need to add dummy
  adaptor sequence XXX

dpastling/plethora,dpastling/cnv_pipeline,dpastling/cnv_pipeline,dpastling/plethora,dpastling/plethora