Update documentation

Author: pdimov

doc/array/changes.adoc

@@ -21,3 +21,4 @@ http://www.boost.org/LICENSE_1_0.txt
 * Removed local `hash_value` overload; `boost::hash` supports array-like types natively.
 * `array<T, 0>` can now be initialized with `= {{}}`.
 * Added `operator\<\=>`.
+* Added `to_array`.

doc/array/reference.adoc

@@ -42,6 +42,13 @@ namespace boost {
     constexpr T& get(array<T, N>&) noexcept;
   template<std::size_t Idx, typename T, std::size_t N>
     constexpr const T& get(const array<T, N>&) noexcept;
+
+  template<class T, std::size_t N>
+    constexpr array<T, N> to_array( T const (&)[N] );
+  template<class T, std::size_t N>
+    constexpr array<T, N> to_array( T (&&)[N] );
+  template<class T, std::size_t N>
+    constexpr array<T, N> to_array( T const (&&)[N] );
 }
 ```
 
@@ -417,3 +424,29 @@ Mandates: :: `Idx < N`.
 Returns: :: `arr[Idx]`.
 
 ---
+
+
+### Creation
+
+```
+template<class T, std::size_t N>
+  constexpr array<T, N> to_array( T const (&a)[N] );
+```
+[horizontal]
+Returns: :: an `array<T, N>` `r` such that for each `i` in `[0..N)`, `r[i]` is copied from `a[i]`.
+
+```
+template<class T, std::size_t N>
+  constexpr array<T, N> to_array( T (&&a)[N] );
+```
+[horizontal]
+Returns: :: an `array<T, N>` `r` such that for each `i` in `[0..N)`, `r[i]` is moved from `std::move(a[i])`.
+
+```
+template<class T, std::size_t N>
+  constexpr array<T, N> to_array( T const (&&a)[N] );
+```
+[horizontal]
+Returns: :: an `array<T, N>` `r` such that for each `i` in `[0..N)`, `r[i]` is copied from `a[i]`.
+
+---