Improvements to increase code coverage:

* Don't include the test code in coverage reports
* Add test code for missing coverage

Other:

* Improve the README.md
* Fix warning in sha1_context
* Tidy up the examples use of namespaces
* Various fixes to documentation and javadocs

test/prepare_buffers.cpp

@@ -87,10 +87,26 @@ public:
         expect(buffer_copy(pbc, cb) == 0);
     }
 
+    void testIterator()
+    {
+        using boost::asio::const_buffer;
+        char b[3];
+        std::array<const_buffer, 3> bs{{
+            const_buffer{&b[0], 1},
+            const_buffer{&b[1], 1},
+            const_buffer{&b[2], 1}}};
+        auto pb = prepare_buffers(2, bs);
+        std::size_t n = 0;
+        for(auto it = pb.end(); it != pb.begin(); --it)
+            ++n;
+        expect(n == 2);
+    }
+
     void run() override
     {
         testBuffers();
         testNullBuffers();
+        testIterator();
     }
 };