Provide complete grade_this_table() and grade_this_vector() functions

[gadenbuie]

If we're going to remove the idea of inconsequential differences as in #76, I think we should go all the way and even provide a grade_this_table() or grade_this_vector() function.

Following up with the comment #71 (comment) it would look something like

grade_this_table <- function(
  expr,
  correct = "Message when correct",
  incorrect = "Message when incorrect",
  ...,
  # all the arguments from tbl_grade_table() except object/expected
  max_diffs = 3,
  check_class = TRUE,
  check_names = TRUE,
  check_dimensions = TRUE,
  check_groups = TRUE,
  check_columns = TRUE,
  check_column_class = check_columns,
  check_column_values = check_columns
) {
  # expr lets users add extra checks or grading code
  
  # ... prep check env and things
  
  function(check_env) {
    grade_this({
      # pass immediately if they're *exactly* the same
      pass_if_equal(correct)
      
      # check for problems with the table
      tbl_grade_table(
        # fill in values from grade_this_table()
      )
      
      # evaluate extra checks in `expr` here
      
      # finally, fail()
      fail(incorrect)
    })
  }
}