UKB.COVID19 0.1.0

Major changes

Improved the test files in test/testhtat/.
Changed a few function names: risk.factor() to risk_factor(), comorbidity.asso() to comorbidity_asso(), comorbidity.summary() to comorbidity_summary(), data.reform() to data_reform().
Removed the argument for output file name in risk_factor(), comorbidity_asso(), comorbidity_summary(), and makePhentypes(). The functions only return objects but not output files. Users can choose if they want to wrtie the outputs into files and can custmise the output files by themselves.
Added in risk_factor() cheching ukb.tab file and return error messages if the file doesn’t include the fields needed for the analyses.
Defined returned objects under S3 class.