Update CodonTable for apparently new NCBI release.

Based on [this Biostars post](https://www.biostars.org/p/105805/) I realized that the codon tables needed to be updated. Using the inline commented code from `Bio.Data.CodonTable` I parsed the new *Pterobranchia Mitochondrial* table and revised the update comment. Note that it seems NCBI has updated `ftp://ftp.ncbi.nih.gov/entrez/misc/data/gc.prt` without incrementing the release number.