Create filterFPKM.R

Filters counts file used in differential expression analysis (e.g. using EdgeR or DESeq) by constructing logFPKM distribution and removing the bottom x% most lowly abundant transcripts. The method is a single function, takes a single count table with multiple conditions and separately tests each condition for abundance distribution, then takes all genes for which evidence of being above the user-specified percentage abundance and outputs a count table for those transcripts.