Performance Pass

strings.Contains and strings.Split seem to be using up a much larger amount of execution time than I was hoping for.  So I changed the processes to use IndexRune wherever possible, which seems to have sped everything up nicely.
Second Performance Pass

Updated the accept matching logic to attempt a simple matching if the passed in Accept header is simple enough.  This makes GetCodecForResponding roughly 500 nanoseconds faster for simple Accept headers (executing in about 200 nanoseconds total as a best case).