set_contents() is a convenience function to change the cell contents of a huxtable within
a dplyr chain. set_contents(ht, x, y, foo) just calls ht[x, y] <- foo and returns ht.
Usage
contents(ht)
contents(ht) <- value
set_contents(ht, row, col, value )
map_contents(ht, row, col, fn)