Add first producer test

include/cppkafka/buffer.h

@@ -2,6 +2,7 @@
 #define CPPKAFKA_BUFFER_H
 
 #include <cstddef>
+#include <algorithm>
 
 namespace cppkafka {
 
@@ -11,6 +12,11 @@ public:
 
     Buffer();
     Buffer(const DataType* data, size_t size);
+    template <typename ForwardIterator>
+    Buffer(const ForwardIterator& start, const ForwardIterator& end) :
+        data_((const DataType*)&*start), size_(std::distance(start, end)) {
+
+    }
 
     Buffer(const Buffer&) = delete;
     Buffer(Buffer&&) = default;
@@ -19,8 +25,10 @@ public:
 
     const DataType* get_data() const;
     size_t get_size() const;
+
+    std::string as_string() const;
 private:
-    const unsigned char* data_;
+    const DataType* data_;
     size_t size_;
 };