Round digits in print.skim_df

[ben-schwen]

Closes #479

Added an additional argument round_early = TRUE to print.skim_df. If round_early is TRUE all doubles in the skim_df are rounded with round(skim_df, 4) before printing.

[elinw]

We have spent a lot of time thinking about rounding and significant digits and also about many possible parameters that we could add. In particular in the case of digits we've thought about whether all of the numerics should get the same number of digits or not. This is especially something we are aware of since one purpose of skimr is to work in undergraduate courses. One question would be why you wouldn't use the API to define the specific way that you want rounding handled.

Also, are you saying you really don't care about the skim object here, just about controlling the printing?

[elinw]

It has been about a month with no response ... i think maybe we need to document how to customize rounding.