docs: expand embedding API, functions, lists, maps, and looping documentation with examples and clarifications

doc/site/functions.markdown

@@ -1,7 +1,7 @@
 ^title Functions
 ^category types
 
-No self-respecting language today can get by without functions—first class little bundles of code. Since Wren is object-oriented, most of your code will live in methods on classes, but free-floating functions are still useful.
+No self-respecting language today can get by without functions—first class little bundles of code. Since Wren is object-oriented, most of your code will live in methods on classes, but free-floating functions are still eminently handy.
 
 Functions are objects like everything else in Wren, instances of the `Fn` class.
 
@@ -9,7 +9,7 @@ Functions are objects like everything else in Wren, instances of the `Fn` class.
 
 Most of the time you create a function just to pass it to some method. For example, if you want to filter a [list](lists.html) by some criteria, you'll call its `where` method, passing in a function that defines the predicate you're filtering on.
 
-Since that's the most common usage pattern, Wren's syntax optimizes for that. Taking a page from Ruby, a function is created by passing a *block argument* to a method. At it's simplest, it looks like this:
+Since that's the most common usage pattern, Wren's syntax optimizes for that. Taking a page from Ruby, a function is created by passing a *block argument* to a method. At its simplest, it looks like this:
 
     :::dart
     blondie.callMe {
@@ -106,7 +106,7 @@ Otherwise, the body returns `null` by default. You can explicitly return a value
 
 ## Closures
 
-As you expect, functions are closures: they can access variables defined outside of their scope. They will hold onto closed-over variables even after leaving the scope where the function is defined:
+As you expect, functions are closures—they can access variables defined outside of their scope. They will hold onto closed-over variables even after leaving the scope where the function is defined:
 
     :::dart
     class Counter {
@@ -116,7 +116,7 @@ As you expect, functions are closures: they can access variables defined outside
       }
     }
 
-Here, the `create` method returns the function created on its second line. That function references a variable `i` declared outside of the function. Even after the function is returned from `create`, it is still able to access `i`.
+Here, the `create` method returns the function created on its second line. That function references a variable `i` declared outside of the function. Even after the function is returned from `create`, it is still able to read and assign to`i`:
 
     :::dart
     var counter = Counter.create