Progress towards #3, fixes #2, fixes #9
 - uses a reputable web site to scrape (annual) ICD-9-CM chapters, sub chapters and headings for majors, all of which are missing. Tests for results.
 - function to convert chapters directory to a comorbidity mapping
 - utility strPairMatch, creates named list from a regex and vector
 - small vignette update, but needs more work to demonstrate new functions