Feature: allow to passing any init parameters to FCGI::ProcManager::XXX

When I tried to use  FCGI::ProcManager::Dynamic as custom proc manager, 
I found then has no possibility to set most important FCGI::ProcManager::Dynamic options like min_nproc, max_proc, delta_nproc.. 

And I add "manager_args" parameter then passed to FCGI::ProcManager::XXX->new(..).

And now easy set any paramenters from command-line:

plackup XXX -s FCGI  --manager FCGI::ProcManager::Dynamic --manager_args "min_nproc 4 max_nproc 40 delta_nproc 5"