Added documentation for advance and distance. Various cleanup and fixes.

- Fixed multiple broken links to the documentation. Converted some of the
  links to internal references to the QuickBook documentation. Not all
  links converted because some of the QuickBook pages are not completely
  converted.
- Renamed utilities.qbk to type_traits.qbk and removed the part duplicated
  by concept_checking.qbk.
- Renamed traits.qbk to iterator_traits.qbk to better disambiguate with
  other type traits documented in type_traits.qbk.
- Converted some of the headings in iterator concepts to sections to be
  able to give those sections ids. This allows to reference those sections
  from other places in the documentation.
- In order to preserve the more compact pagination of the new sections
  (i.e. to have multiple sections on one page, like it was with headings)
  set chunk.section.depth=2 in the docs Jamfile.

doc/quickbook/algorithms.qbk

@@ -1,12 +1,96 @@
 [section:algorithms Algorithms]
 
+[section:advance Function template `advance()`]
+
+The `boost::iterators::advance` function template is an adapted version of `std::advance` for the Boost iterator [link iterator.concepts.concepts_traversal traversal concepts].
+
+[heading Header]
+
+    <boost/iterator/advance.hpp>
+
+[heading Synopsis]
+
+    template <typename Iterator, typename Distance>
+    constexpr void advance(Iterator& it, Distance n);
+
+
+[heading Description]
+
+Moves `it` forward by `n` increments (or backward by `|n|` decrements if `n` is negative).
+
+[heading Requirements]
+
+`Iterator` should model Incrementable Iterator.
+
+[heading Preconditions]
+
+Let `it`[sub `i`] be the iterator obtained by incrementing (or decrementing if `n` is negative) `it` by `i`. All the iterators `it`[sub `i`] for `i` = 0, 1, 2, ..., `|n|` should be valid.
+
+If `Iterator` does not model [link iterator.concepts.concepts_traversal.bidirectional Bidirectional Traversal Iterator], `n` should be non-negative.
+
+[heading Complexity]
+
+If `Iterator` models [link iterator.concepts.concepts_traversal.random_access Random Access Traversal Iterator], it takes constant time; otherwise it takes linear time.
+
+[heading Notes]
+
+* This function is not a customization point and is protected against being found by argument-dependent lookup (ADL).
+* This function is `constexpr` only in C++14 or later.
+
+[heading Acknowledgements]
+
+Contributed by Michel Morin.
+
+[endsect]
+
+[section:distance Function template `distance()`]
+
+The `boost::iterators::distance` function template is an adapted version of `std::distance` for the Boost iterator [link iterator.concepts.concepts_traversal traversal concepts].
+
+[heading Header]
+
+    <boost/iterator/distance.hpp>
+
+[heading Synopsis]
+
+    template <typename Iterator>
+    constexpr typename iterator_difference<Iterator>::type
+    distance(Iterator first, Iterator last);
+
+[heading Description]
+
+Computes the (signed) distance from `first` to `last`.
+
+[heading Requirements]
+
+`Iterator` should model [link iterator.concepts.concepts_traversal.single_pass Single Pass Iterator].
+
+[heading Preconditions]
+
+If `Iterator` models [link iterator.concepts.concepts_traversal.random_access Random Access Traversal Iterator], `[first, last)` or `[last, first)` should be valid; otherwise `[first, last)` should be valid.
+
+[heading Complexity]
+
+If `Iterator` models [link iterator.concepts.concepts_traversal.random_access Random Access Traversal Iterator], it takes constant time; otherwise it takes linear time.
+
+[heading Notes]
+
+* This function is not a customization point and is protected against being found by argument-dependent lookup (ADL).
+* This function is `constexpr` only in C++14 or later.
+
+[heading Acknowledgements]
+
+Contributed by Michel Morin.
+
+[endsect]
+
 [section:next_prior Function templates `next()` and `prior()`]
 
 Certain data types, such as the C++ Standard Library's forward and bidirectional iterators, do not provide addition and subtraction via `operator+()` or `operator-()`. This means that non-modifying computation of the next or prior value requires a temporary, even though `operator++()` or `operator--()` is provided. It also means that writing code like `itr+1` inside a template restricts the iterator category to random access iterators.
 
 The `next()` and `prior()` functions defined in `boost/next_prior.hpp` provide a simple way around these problems.
 
-[section Synopsis]
+[heading Synopsis]
 
     template <class T>
     T next(T x)
@@ -36,7 +120,7 @@ The `next()` and `prior()` functions defined in `boost/next_prior.hpp` provide a
 
 [note Function implementations above are given for exposition only. The actual implementation has the same effect for iterators, but has different properties, as documented later.]
 
-[endsect]
+[heading Usage]
 
 Usage is simple:
 
@@ -56,12 +140,10 @@ First, `boost::next()` and `boost::prior()` are compatible not only with iterato
 
 Second, `boost::next()` and `boost::prior()` use [link iterator.concepts.concepts_traversal traversal categories] to select the most efficient implementation. For some kinds of iterators, such as [link iterator.specialized.transform transform iterators], the standard iterator category does not reflect the traversal category correctly and therefore `std::next()` and `std::prev()` will fall back to linear complexity.
 
-[section Acknowledgements]
+[heading Acknowledgements]
 
 Contributed by [@http://www.boost.org/people/dave_abrahams.htm Dave Abrahams]. Two-argument versions by Daniel Walker.
 
 [endsect]
 
 [endsect]
-
-[endsect]