[stdlib] Revise stdlib documentation comments

- Expand pre-example explanations
- Update documentation for SE-0118
- Removing remaining 'iff' usage
- Revise Array discussion
- Fix formIndex(_:offsetBy) parameter formatting
- Improve index/formIndex(_:offsetBy:(limitedBy:)?) discussion
- Update Quick Look discussions
- Fixes grammar inconsistencies
- Adds parameter / return documentation
- Adds and expands on examples
- Revises AnyObject discussion for new `id` bridging rules
- Revise readLine, print, and assertion functions
- Add missing docs to String index-moving methods

stdlib/public/core/Algorithm.swift

@@ -10,9 +10,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-/// Returns the lesser of `x` and `y`.
+/// Returns the lesser of two comparable values.
 ///
-/// If `x == y`, returns `x`.
+/// - Parameters:
+///   - x: A value to compare.
+///   - y: Another value to compare.
+/// - Returns: The lesser of `x` and `y`. If `x` is equal to `y`, returns `x`.
 public func min<T : Comparable>(_ x: T, _ y: T) -> T {
   // In case `x == y` we pick `x`.
   // This preserves any pre-existing order in case `T` has identity,
@@ -23,7 +26,13 @@ public func min<T : Comparable>(_ x: T, _ y: T) -> T {
 
 /// Returns the least argument passed.
 ///
-/// If there are multiple equal least arguments, returns the first one.
+/// - Parameters:
+///   - x: A value to compare.
+///   - y: Another value to compare.
+///   - z: A third value to compare.
+///   - rest: Zero or more additional values.
+/// - Returns: The least of all the arguments. If there are multiple equal
+///   least arguments, the result is the first one.
 public func min<T : Comparable>(_ x: T, _ y: T, _ z: T, _ rest: T...) -> T {
   var minValue = min(min(x, y), z)
   // In case `value == minValue`, we pick `minValue`. See min(_:_:).
@@ -33,9 +42,12 @@ public func min<T : Comparable>(_ x: T, _ y: T, _ z: T, _ rest: T...) -> T {
   return minValue
 }
 
-/// Returns the greater of `x` and `y`.
+/// Returns the greater of two comparable values.
 ///
-/// If `x == y`, returns `y`.
+/// - Parameters:
+///   - x: A value to compare.
+///   - y: Another value to compare.
+/// - Returns: The greater of `x` and `y`. If `x` is equal to `y`, returns `y`.
 public func max<T : Comparable>(_ x: T, _ y: T) -> T {
   // In case `x == y`, we pick `y`. See min(_:_:).
   return y >= x ? y : x
@@ -43,7 +55,13 @@ public func max<T : Comparable>(_ x: T, _ y: T) -> T {
 
 /// Returns the greatest argument passed.
 ///
-/// If there are multiple equal greatest arguments, returns the last one.
+/// - Parameters:
+///   - x: A value to compare.
+///   - y: Another value to compare.
+///   - z: A third value to compare.
+///   - rest: Zero or more additional values.
+/// - Returns: The greatest of all the arguments. If there are multiple equal
+///   greatest arguments, the result is the last one.
 public func max<T : Comparable>(_ x: T, _ y: T, _ z: T, _ rest: T...) -> T {
   var maxValue = max(max(x, y), z)
   // In case `value == maxValue`, we pick `value`. See min(_:_:).
@@ -53,18 +71,20 @@ public func max<T : Comparable>(_ x: T, _ y: T, _ z: T, _ rest: T...) -> T {
   return maxValue
 }
 
-/// The iterator for `EnumeratedSequence`.  `EnumeratedIterator`
-/// wraps a `Base` iterator and yields successive `Int` values,
-/// starting at zero, along with the elements of the underlying
-/// `Base`:
+/// The iterator for `EnumeratedSequence`.
+///
+/// An instance of `EnumeratedIterator` wraps a base iterator and yields
+/// successive `Int` values, starting at zero, along with the elements of the
+/// underlying base iterator. The following example enumerates the elements of
+/// an array:
 ///
 ///     var iterator = ["foo", "bar"].enumerated().makeIterator()
 ///     iterator.next() // (0, "foo")
 ///     iterator.next() // (1, "bar")
 ///     iterator.next() // nil
 ///
-/// - Note: Idiomatic usage is to call `enumerate` instead of
-///   constructing an `EnumerateIterator` directly.
+/// To create an instance of `EnumeratedIterator`, call
+/// `enumerated().makeIterator()` on a sequence or collection.
 public struct EnumeratedIterator<
   Base : IteratorProtocol
 > : IteratorProtocol, Sequence {
@@ -91,14 +111,22 @@ public struct EnumeratedIterator<
   }
 }
 
-/// The type of the `enumerated()` property.
+/// An enumeration of the elements of a sequence or collection.
 ///
-/// `EnumeratedSequence` is a sequence of pairs (*n*, *x*), where *n*s
-/// are consecutive `Int`s starting at zero, and *x*s are the elements
-/// of a `Base` `Sequence`:
+/// `EnumeratedSequence` is a sequence of pairs (*n*, *x*), where *n*s are
+/// consecutive `Int` values starting at zero, and *x*s are the elements of a
+/// base sequence.
+///
+/// To create an instance of `EnumeratedSequence`, call `enumerated()` on a
+/// sequence or collection. The following example enumerates the elements of
+/// an array.
 ///
 ///     var s = ["foo", "bar"].enumerated()
-///     Array(s) // [(0, "foo"), (1, "bar")]
+///     for (n, x) in s {
+///         print("\(n): \(x)")
+///     }
+///     // Prints "0: foo"
+///     // Prints "1: bar"
 public struct EnumeratedSequence<Base : Sequence> : Sequence {
   internal var _base: Base
 
@@ -108,8 +136,6 @@ public struct EnumeratedSequence<Base : Sequence> : Sequence {
   }
 
   /// Returns an iterator over the elements of this sequence.
-  ///
-  /// - Complexity: O(1).
   public func makeIterator() -> EnumeratedIterator<Base.Iterator> {
     return EnumeratedIterator(_base: _base.makeIterator())
   }