Adding head circumference from the WHO

Use "hcfa".

Note: Head circumference only applies to infants and toddlers, and is represented here up to age 5.
Fixing a bug
Merge remote-tracking branch 'upstream/master'

Conflicts:
	pygrowup/pygrowup.py
Correcting data tables for CDC female charts

Some values were incorrect due to a bug in my previous conversion script. These should be accurate.
Merge pull request #4 from mjacksonw/master

Correcting CDC growth chart data