Uppdate changelog with new section for v1.16

CHANGELOG.md

 ## Changes for next release
 
  * To be defined
+
+
+## Robotran v1.16.0
+
  * [C][Python] error handling is enhanced, with new error names and proper closing of the functions for all modules, except Real-time in dirdyn
  * [C] All user models are printed with the `mbs_print_data` function
  * [C] New function `print_d_vec_0_format` allowing to set the format of the vector values.