docs: reflow all markdown files to 80-char width and add control-flow page with branching/looping content

doc/site/values.markdown

@@ -3,15 +3,20 @@
 
 Values are the built-in object types that all other objects are composed of.
 They can be created through *literals*, expressions that evaluate to a value.
+All values are *immutable*—once created, they do not change. The number
+`3` is always the number `3`. The string `"frozen"` can never have its
+character array modified in place.
 
 ## Booleans
 
 A boolean value represents truth or falsehood. There are two boolean literals,
-`true` and `false`. Its class is `Bool`.
+`true` and `false`. Their class is `Bool`.
 
 ## Numbers
 
-Like other scripting languages, Wren has a single numeric type: double-precision floating point. Number literals look like you expect coming from other languages:
+Like other scripting languages, Wren has a single numeric type:
+double-precision floating point. Number literals look like you expect coming
+from other languages:
 
     :::dart
     0
@@ -25,33 +30,48 @@ Numbers are instances of the `Num` class.
 
 ## Strings
 
-Strings are chunks of text. String literals are surrounded in double quotes:
+Strings are chunks of text stored as UTF-8. Their class is `String`. String
+literals are surrounded in double quotes:
 
     :::dart
     "hi there"
 
-A couple of escape characters are supported:
+A handful of escape characters are supported:
 
     :::dart
-    "\n" // Newline.
     "\"" // A double quote character.
     "\\" // A backslash.
+    "\a" // Alarm beep. (Who uses this?)
+    "\b" // Backspace.
+    "\f" // Formfeed.
+    "\n" // Newline.
+    "\r" // Carriage return.
+    "\t" // Tab.
+    "\v" // Vertical tab.
 
-Their class is `String`.
+A `\u` followed by four hex digits can be used to specify a Unicode code point.
 
 ## Ranges
 
-A range is a little object that represents a consecutive range of numbers. They don't have their own dedicated literal syntax. Instead, the number class implements `..` and `...` operators to create them:
+A range is a little object that represents a consecutive range of integers.
+They don't have their own dedicated literal syntax. Instead, the number class
+implements the `..` and `...` [operators](expressions.html#operators) to create
+them:
 
     :::dart
     3..8
 
-This creates a range from three two eight, including eight itself. If you want a half-inclusive range, use `...`:
+This creates a range from three to eight, including eight itself. If you want a
+half-inclusive range, use `...`:
 
     :::dart
     4...6
 
-This creates a range from four to six *not* including six itself. Ranges are commonly used for [looping](looping.html) over a sequences of numbers, but are useful in other places too. You can pass them to a [list](lists.html)'s subscript operator to return a subset of the list, for example:
+This creates a range from four to six *not* including six itself. Ranges are
+commonly used for [iterating](control-flow.html#for-statements) over a
+sequences of numbers, but are useful in other places too. You can pass them to
+a [list](lists.html)'s subscript operator to return a subset of the list, for
+example:
 
     :::dart
     var list = ["a", "b", "c", "d", "e"]
@@ -60,7 +80,7 @@ This creates a range from four to six *not* including six itself. Ranges are com
 
 ## Null
 
-Wren has a special value `null`, which is the only instance of the class `Null`.
-(Note the difference in case.) It functions a bit like `void` in some
+Wren has a special value `null`, which is the only instance of the class
+`Null`. (Note the difference in case.) It functions a bit like `void` in some
 languages: it indicates the absence of a value. If you call a method that
 doesn't return anything and get its returned value, you get `null` back.