add_factor_order: Add 'hclust' order to columns.
In allydunham/tblhelpr: Common Opperations for Tibbles

Add orders to two character columns in a tibble, based on heirarchical clustering of a third column.

1	add_factor_order(tbl, col1, col2, value, sym = FALSE)

`tbl`	A tibble.
`col1, col2`	Columns to add order to.
`value`	Column giving a value from each pair of levels in `col1` and `col2`.
`sym`	Is the relationship between `col1` and `col2` symetric. Meaning they represent the same physical property and the expanded matrix of value pairs will be symetrical across the diagonal.