Adds new function cliui.DisplayTable(items []T, sortBy string, filterColumns []string) (string, error) which will render a table and return it as a string.

Uses the reflect package to sniff the columns using a table:"name" struct tag. If any of the input types are invalid, this will always panic (even for empty slices!). The input must be a slice or a pointer to a slice that concretely holds a single struct type or a pointer to a struct type. The inner struct type must have at least one table:"name" tag. ,recursive cannot be specified if the field is not a struct or a pointer to a valid tableable struct.

Gist of how it works:

1. Ensure the input type is a slice or a pointer to a slice (as it's really an interface{} input type to avoid generics clutter in the output binary)
2. Look at the type that is contained in the slice (even if it's empty or nil) to figure out what columns exist so we can render a header
   1. Ensure it's a struct or a pointer to a struct
   2. Iterate over every field and append to a list the name of the field
   3. If we encounter a field with the tag table:"name,recursive":
      1. Ensure the field's type is a struct or a pointer to a struct
      2. Repeat step 2 but capture in a separate list
      3. Append to the parent's column list, but append the parent field name from 2.3 like so: "$ParentName $ChildName"
   4. Return a []string containing the column names for the table
3. Iterate over every value in the slice and convert to map[string]interface{}, a map of column names to values
4. Print the table values by checking for the columns in each value's map, or printing <nil> if the value is not present in the map