introduce optional callback to report progress of long running optimizatinos
Merge branch 'master' of github.com:smee/cobyla2 into webworker

Conflicts:
	Cobyla.js
[fix] typo during merge fixing
[feature] add flag for premature abort
Introduce explicit  status, remove stop flag, does not work in webworkers
[fix] transmit optimized x values in the final status