as_grade_list: constructor function for a grade object
In adsteen/gradr:

constructor function for a grade object

1 2	as_grade_list(x, id.col = lastname, raw.grade.col = raw.grade, adj.grade.col = NULL)

`x`	data frame that contains a vector of names (or other IDs) and a vector of grades
`id.col`	column that contains unique identifiers for students (e.g. last name)
`raw.grades.col`	column that contains raw grades
`adj.grades.col`	column that contains adjusted grades (this will usually be left as the default NULL)