Add the autohide argument to cols_nanoplot()

[rich-iannone]

This adds the autohide argument to the cols_nanoplot() function. As in several other cols_*() functions, there is the autohide argument to automatically hide columns that participate as input but become redundant after the function is invoking.

In this case, inputs to cols_nanoplot() provide data for the nanoplot in a separate column. Once the plot is made, the data in the input column(s) is likely going to require a separate cols_hide() call to hide the columns providing the input. We can save the trouble in doing so with the autohide = TRUE default (same default for all functions having an autohide argument). For those cases where the input column should remain visible, the user is able to set autohide = FALSE.