Improve the information provided on each function

[RobertASmith]

Easy:

• Add ability to identify solo functions (functions with no child or parent) in the summary table, by adding a new column with a logical (1/0) for solo.

Moderate:

• Add ability to identify which external packages are used in each function (e.g. ggplot2, zoo) (answer may be none). This could then be added to the information on the function - it is useful to see where the dependencies are in the model. This is a seperate issue Add external dependencies #59
• Add the length (number of lines) of each function to the summary table. @Smit-tay could you look into this, it will enable us to size the nodes in the visual by some transformation (probably log) of the number of lines in the function.

Can do this easily for a loaded function by character? although not sure this is the best way.

body(rowSums)  |> nchar() |> sum()

• Add the number of arguments the function takes to the summary table

Hard:

• Add ability to classify types of functions, assign different shapes to these.
• Add the ability to search for a key word in any function.