Future versions of icd will drop
the icd_ prefix. For example, charlson should be used in
favor of icd_charlson. To distinguish icd function calls,
consider using the namespace prefix icd:: instead, e.g.,
icd::charlson. Functions which specifically operate on either ICD-9
or ICD-10 codes or their subtypes will retain the prefix. E.g.
icd9_comorbid_ahrq. icd specific classes also retain
the prefix, e.g., icd_wide_data.