get_icd_history         Returns a data frame with ICD transition
                        history, consisting of year, ICD code and
                        label. Optional arguments allow selection of
                        entries by year or ICD code. This is beneficial
                        because the entire history is relatively large
                        and rarely required in full.
get_icd_labels          Returns a data frame with ICD metadata,
                        consisting of year, ICD code and label.
                        Optional arguments allow selection of entries
                        by year, code or label. This is beneficial
                        because the entire history is relatively large
                        and rarely required in full.
icd_expand              Expand list of ICD codes to include all
                        possible subcodes
icd_history             Historize a list of ICD codes to cover the
                        specified years
icd_meta_blocks         Metadata for the ICD-10-GM code blocks
icd_meta_chapters       Metadata for the ICD-10-GM chapters
icd_meta_codes          Metadata for all ICD-10-GM codes
icd_meta_transition     Transition between ICD-10-GM versions
icd_parse               Extract all ICD codes from a character vector
icd_showchanges         Show all changes in ICD history relating to the
                        3-digit codes contained in the data.frame
                        icd_in. The output of icd_expand can be passed
                        directly to this function to display relevant
                        changes.
icd_showchanges_icd3    Show all changes in ICD history relating to the
                        3-digit codes contained in a given vector icd
is_icd_code             Test whether a string is a valid ICD code
