make sure we document and test all ways of creating a recipe

[EmilHvitfeldt]

the following

recipe(data.frame)

recipe(data.frame, vars = vars, roles = roles)

recipe(data.frame, vars = formula)

recipe(formula, data.frame)

recipe(matrix)

recipe(matrix, vars = vars, roles = roles)

recipe(matrix, vars = formula)

I'm not including recipe(formula, matrix) because it is too similar to recipe(formula, data.frame) because we just call as_tibble() on it