initial spike for apply_model started
col_name: returns NULL if passed NULL
functions added: compact, lookup_name, is.character0, `%||%`
README updated in accordance with changes
for `as.fitted_frame` use `class_estimate_map` to define a map
new structure of storing column groups, and helper functions utilised
roc debugging
`resp_val<-` added
`apply_model` updated so that response_name and class_estimate_map can be defined in call
doc update
exports: `as.model_frame`, `as.fitted_frame`, `apply_model_`, `cbind.model_frame`, `class_estimate_map`