clip_primers: Clip primers using cutadapt
In ucvm/nemabiomeR: Helper functions to run the dada2 pipeline on nemabiome data

Uses the external cutadapt progrom to trim off primer sequences

1 2	clip_primers(fwd_files, rev_files, fwd_primer, rev_primer, out_dir, cutadapt_bin, samples = NULL, max_n = 0, q = 20, min_len = 50)

`fwd_files`	list of file names of the forward reads
`rev_files`	list of file names of the reverse reads
`fwd_primer`	forward primer sequnce as a string
`rev_primer`	reverse primer sequnce as a string
`out_dir`	path to directory to write the clipped files
`cutadapt_bin`	location of the cutadapt binary. If you're not sure, run `which cutadapt` on the command line to find out
`samples`	character vector of samples names, if not provided the the forward file names will be used
`max_n`	discard reads with more than this many Ns
`q`	quality score for 3' end-trimming
`min_len`	minimum length of sequence to retain