Updates combining-maps recipe

Edits Solution section to be more concise. Adds another example. Updates
discussion section to be more concise and accurate.
Updates creating-a-map

Edited to be more concise and for accuracy. Cross-reference Comparators
instead of going into detail here.
Updates creating-a-map to use 'you want to' language
Corrects wording of problem in creating-a-map
Updates creating-a-set recipe