MatSize::operator()() supports only 2-d matrices.

The following data types for attributes are implemented:
 - int
 - double
 - cv::String
 - cv::InputArray

- Fixed a typo in the help text
- Fixed a typo in a comment line

 - Some test cases are added
 - Two tutorials are written to show how to use it.

to prevent console spam. only outputs errors/ warnings now.

'(k * (ww) + ii)' overrun allocated buffer (k = height - 1, ii = ww)

- uninitialized variable 'previous_size'
- incorrect Mat element access pattern via address arithmetic

- descriptor Mat access unsigned -> int
- do not use types uint8_t, etc. from C++11
- fixed uninitialized memory access
- minor cosmetic modifications