allow using start instead of psexec in parallel runs under windows

For local clusters only, allow using start instead of psexec with windows, to properly allocate affinity when there are more than 32 cores. Manual updated accordingly.

It would require an additional parallel option in dynare invocation: parallel_use_psexec=INTEGER, which triggers the options_ field options_.parallel_info.use_psexec.

if parallel_use_psexec=1 (or default):

options_.parallel_info.use_psexec = true;

otherwise

options_.parallel_info.use_psexec = false;