Usefull function to return the reason why the geometry is not valid

This function is similar to http://postgis.net/docs/ST_IsValidReason.html.


```mysql
SELECT ST_IsvalidReason('POLYGON ((280 330, 120 200, 360 190, 352 197, 170 290, 280 330))'::GEOMETRY);

--Returns 
--Self-intersection at or near point (207.3066943435392, 270.9366891541256, NaN)


```