Complete makeover - out with old deyo/elixhauser/ahrq and in with cmrbdt.calc

This is a complete makeover of the original comorbidity-package. The functions have been tested extensively using the testthat-package and used on actual large data-sets.

Rewritten comorbidities-package

This is a rewrite version of Paul Gerrard's comorbidities package. It also contains important bug-fixes, see NEWS-file for details.