Method append

libhsclient/string_buffer.hpp:93–98

    append(str, str + N - 1);
  }
  void append(const char *start, const char *finish) {
    const size_t len = finish - start;
    reserve(size() + len);
    memcpy(buffer + end_offset, start, len);
    end_offset += len;
  }
  void append_2(const char *s1, const char *f1, const char *s2,
    const char *f2) {
    const size_t l1 = f1 - s1;