Added class DrivenEngine (no implementation yet)

luprex/core/cpp/streambuffer.cpp

@@ -45,6 +45,10 @@ int64_t StreamBuffer::fill() const {
     return write_cursor_ - read_cursor_;
 }
 
+const char *StreamBuffer::data() const {
+    return read_cursor_;
+}
+
 bool StreamBuffer::layout_is(int64_t a, int64_t b, int64_t c) {
     if (read_cursor_ - buf_lo_ != a) return false;
     if (write_cursor_ - read_cursor_ != b) return false;