Bug fixes and new features.

Fixed an issue whereby edits at the beginning of a sequence would cause a crash
because the mRNA sequence did no possess a complete codon. Also started a new
line of the main program to calculate gross stats by gene over the entire organism.
Changed summary statistics to single output file.

Program is intended to be run on groups of infiles, for which summary stats
by gene will be output to a separate csv file from detailed stats by gene,
which will be individual csv files. Added new summary stats such as GC content,
sequence lengths, and percent edits in codon positions.