Determines trinucleotide context fraction from a mutation counts list. Given
a data frame or .txt file or mutation counts with columns as trincucleotide
contexts in the form A[C>A]A and the rows as sample id's and a data frame or
.txt file of the times each tri nucleotide context is seen in the sequencing
region with the rows in the format ACA, the function returns a data frame of
the mutation counts normalized by trinucleotide frequency