Fix Age Groupings for cases of 1-5 years listed as option (Total Blood Mercury)

For Total Blood Mercury the age groupings are different 1-5 (rather than 3 to 5), 6-11, 12-19, and 20+.  This is surprisingly different than other age groupings for biomarkers because NHANES generally only looks at 3 years and older. However, it looks like Mercury has specific weights that include 1-11 year old and a one-half sample of 12+ year olds. We should investigate where else this shows up.