[Doc] Write new tutorial sections and reorder other sections

- Write sections on containers, algorithms, and runtime performance
- Make sure examples consistently use 2 space tabs
- Disable -Wunused-parameter for examples
- Resolves #70
  The requirement of pure functions is now documented.
- Resolves #14
  It turns out that the benefits of specifying the type of containers
  seems to be essentially limited to pattern matching. This is not
  enough to justify all the bad things it brings, especially
  considering the fact that recursion (currently the only use
  case for pattern matching) forces the creation of a new tuple
  at each step, which is disastrous. The unspecified-ness of the
  container's type is now documented.

example/tutorial/include_set.cpp

@@ -13,7 +13,7 @@ using namespace boost::hana;
 
 
 int main() {
-    constexpr auto xs = set(1, 2.2, 'x');
-    static_assert(contains(xs, 'x'), "");
+  constexpr auto xs = set(1, 2.2, 'x');
+  static_assert(contains(xs, 'x'), "");
 }
 //! [main]