Version 0.5 - fixes #3
 - explain and condense both now work well
 - distinguish 'real' (in billable codes list) or non-real (only requiring syntactically correctness) in explain and condense. (Not done for ranges yet)
 - return just vector of descriptions for explain: may add ability to get description per code in the future,
 - fixed parsing error which dropped some words for start of multi-word code descriptions.
 - moved condense functions to explain.R
 - added isMajor function to valid.R
 - documentation and tests
 - vignette shows new features, but not yet feature complete
Merge branch 'v0.5dev' of github.com:jackwasey/icd9 into v0.5dev