new converter: nlsp2nlp

I have committed nlsp2nlp converter, see NLSP page for details. It tries to minimize

   ||F(x)||2

and, of course, it is capable of handling constrained problems.

You can try updated nlsp_1.py or nlsp_constrained.py from /examples.

However, a requirement should be satisfied: non-linear functions shouldn't be splitted.

This minor issue is intended to be fixed in future (BTW, splitting can't yield benefits for nlsp2nlp converter with any NLP solver).