All tidying methods return a data.frame without rownames, whose
structure depends on the method chosen.
tidy.aareg returns one row for each coefficient, with
the columns
termname of coefficient
  estimateestimate of the slope
  statistictest statistic for coefficient
  std.errorstandard error of statistic
  robust.serobust version of standard error estimate
  zz score
  p.valuep-value
glance returns a one-row data frame containing
  
statisticchi-squared statistic
  p.valuep-value based on chi-squared statistic
  dfdegrees of freedom used by coefficients