Change data set to dataset (#1282)

- It changes `data set(s)` to `dataset(s)` for consistency, throughout the book.
- It adds `# Left` and `# Right` comments for similar side-by-side plots.

intro.qmd

@@ -57,7 +57,7 @@ Visualizations can surprise you, and they don't scale particularly well because
 **Models** are complementary tools to visualization.
 Once you have made your questions sufficiently precise, you can use a model to answer them.
 Models are a fundamentally mathematical or computational tool, so they generally scale well.
-Even when they don\'t, it\'s usually cheaper to buy more computers than it is to buy more brains!
+Even when they don't, it's usually cheaper to buy more computers than it is to buy more brains!
 But every model makes assumptions, and by its very nature a model cannot question its own assumptions.
 That means a model cannot fundamentally surprise you.
 
@@ -105,7 +105,7 @@ This book doesn't teach data.table because it has a very concise interface that
 However, the performance payoff is well worth the effort required to learn it if you're working with large data.
 
 If your data is bigger than this, carefully consider whether your big data problem is actually a small data problem in disguise.
-While the complete data set might be big, often, the data needed to answer a specific question is small.
+While the complete dataset might be big, often, the data needed to answer a specific question is small.
 You might be able to find a subset, subsample, or summary that fits in memory and still allows you to answer the question that you're interested in.
 The challenge here is finding the right small data, which often requires a lot of iteration.