Version 0.4
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* Present-on-arrival field handled gracefully
* Revised co-morbidity handling, with functions specific to each mapping
* Standardized naming of fields across Elixhauser and Charlson based mappings for clarity, consistency and comparaibility
* Handle mild and severe co-morbidities without double-counting. Fixes issue #23
* Enable magrittr-style piping as option to clarify chains of operations. Issue #5
* many more test cases, including specific tests for individual values in each computed mapping, and also for the new comorbidity functions
* Vignette updated to demonstrate clearer new functions

Version 0.3
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* Addition of several utility functions, mostly kept for internal use, but which clarify the code
* Consistent behavior with invalid codes, allowing ignore, silent conversion to NA, warn with conversion to NA, or stopping.
* Outline of code to read top level ICD-9 definitions from canonical CDC RTF file.
* Progress to
* Made functions magrittr friendly
* Bug fixes, refactoring, more tests
* Include parsing of hierarchy
* Internal function which reads a file from a zip at a URL
* The included pre-parsed data are slightly updated to include some missing top-level numbers when all the children were also present. ("043" %i9s% "04499" should equal "043" %i9s% "044")

Version 0.2.1
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 * trivial changes to appease CRAN

Version 0.2
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* Added more co-morbidity mappings, Elixhauser original and Quan/Elixhauser.
* Exposed more functions to public API
* Better conversion of ICD-9 codes to textual representation
* Expanded vignette
* Bug fixes and test cases
* Improved documentation

Version 0.1.1
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* Include missing import for memoise
* optionally process AHRQ comorbidity subcategories into parent categories
* include the processed binary data. Unlikely to change often, and not too big.


Version 0.1
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* First release. Fully functional, no known bugs, but will benefit from addition of planned features described in README.

