Add the sub_small_vals(), sub_large_vals(), and sub_values() methods

[rich-iannone]

To round out the collection of sub_*() methods, we still need the following:

They are all important because some values provided from data as is would be misleading or plainly wrong. For example, some value that is captured as near zero from an instrument might be rounded down as zero from a formatting method. However, it is incorrect to report zero as there is likely some value but it's below the measurement threshold (e.g., environmental sampling of toxins).

As far motivating examples, we definitely need to have them for all of these methods (especially for sub_values()).