Add idvaluemap container

it is a vector based map, preserving insertion order and providing
completion on ids it contains.

src/idvaluemap.hh

@@ -0,0 +1,89 @@
+#ifndef idvaluemap_hh_INCLUDED
+#define idvaluemap_hh_INCLUDED
+
+namespace Kakoune
+{
+
+template<typename _Id, typename _Value>
+class idvaluemap
+{
+public:
+    typedef std::pair<_Id, _Value> value_type;
+    typedef std::vector<value_type> container_type;
+    typedef typename container_type::iterator iterator;
+    typedef typename container_type::const_iterator const_iterator;
+
+    void append(const value_type& value)
+    {
+        m_content.push_back(value);
+    }
+
+    void append(value_type&& value)
+    {
+        m_content.push_back(value);
+    }
+
+    iterator find(const _Id& id)
+    {
+        for (auto it = begin(); it != end(); ++it)
+        {
+            if (it->first == id)
+                return it;
+        }
+        return end();
+    }
+
+    const_iterator find(const _Id& id) const
+    {
+        for (auto it = begin(); it != end(); ++it)
+        {
+            if (it->first == id)
+                return it;
+        }
+        return end();
+    }
+
+    bool contains(const _Id& id) const
+    {
+        return find(id) != end();
+    }
+
+    void remove(const _Id& id)
+    {
+        for (auto it = m_content.begin(); it != m_content.end(); ++it)
+        {
+            if (it->first == id)
+            {
+                m_content.erase(it);
+                return;
+            }
+        }
+    }
+
+    template<std::string (*id_to_string)(const _Id&)>
+    CandidateList complete_id(const std::string& prefix,
+                              size_t cursor_pos)
+    {
+        std::string real_prefix = prefix.substr(0, cursor_pos);
+        CandidateList result;
+        for (auto& value : m_content)
+        {
+            std::string id_str = id_to_string(value.first);
+            if (id_str.substr(0, real_prefix.length()) == real_prefix)
+                result.push_back(std::move(id_str));
+        }
+        return result;
+    }
+
+    iterator       begin()       { return m_content.begin(); }
+    iterator       end()         { return m_content.end(); }
+    const_iterator begin() const { return m_content.begin(); }
+    const_iterator end()   const { return m_content.end(); }
+
+private:
+    container_type m_content;
+};
+
+}
+
+#endif // idvaluemap_hh_INCLUDED