icd9GetChapters: get ICD-9 Chapters from vector of ICD-9 codes
In jackwasey/icd9: Tools for Working with ICD-9 Codes, and Finding Comorbidities

This runs quite slowly. Used too rarely to be worth optimizing now. This is used to build a master list of ICD-9 codes with their respective chapters, sub-chapters, etc.. The querying of the web page to get these is already done, and the results saved in the lists icd9Chapters etc which define ranges.

1	icd9GetChapters(icd9, isShort = icd9GuessIsShort(icd9), verbose = FALSE)

`icd9`	is a character vector or factor of ICD-9 codes. If fewer than five characters is given in a code, then the digits are greedily assigned to hundreds, then tens, then units, before the decimal parts. E.g. "10" becomes "010", not "0010".
`isShort`	single logical value which determines whether the ICD-9 code provided is in short (TRUE) or decimal (FALSE) form. Where reasonable, this is guessed from the input data.
`verbose`	single logical value, defaults to `FALSE` in most functions.