Changed

• Updated behavior of sd.recenter option to include new NHANES reference medians and explicit specification with "NHANES" or "derive" (mitre#9)
• Switched README.md to be generated from README.Rmd w/knitr (thanks @mcanouil) (#17)
• Switched to use file.path() more consistently in R/growth.R

Added

• Added inst/extdata/nhanes-reference-medians.csv, reference medians for recentering derived from NHANES (described in README)