Merge pull request 'feature/no_std_lib' (#9) from feature/no_std_lib into master

Reviewed-on: http://git.mercurial-manifold.eu/an.tsouchlos/const_fmt/pulls/9

const_fmt/stdlib.h

@@ -240,7 +240,7 @@ public:
     constexpr array(const array&) = default;
     constexpr array(array&&) = default;
 
-    constexpr array& operator=(array& other) = default;
+    constexpr array& operator=(const array& other) = default;
     constexpr array& operator=(array&& other) = default;
 
     constexpr void swap(array<data_t, t_size>& other) noexcept {
@@ -271,6 +271,14 @@ public:
         return (&(m_data[t_size - 1]) + 1);
     }
 
+    constexpr const_iterator begin() const noexcept {
+        return &(m_data[0]);
+    }
+
+    constexpr const_iterator end() const noexcept {
+        return (&(m_data[t_size - 1]) + 1);
+    }
+
     constexpr const_iterator cbegin() const noexcept {
         return &(m_data[0]);
     }