Mean solution errors over 30 independent runs

In addition, reduce the maximal function evaluation set for saving
running time.
Update README.md

Single-objective mixed integer optimization
Add more comments to comparison runner.
10 instances of maxfunevals

10 instances of maxfunevals for each test function, but only 4
independent runs.
Induce comparison mechanism, and refactor it.
Merge pull request #10 from ChinChangYang/develop

Each solver has four independent runs for each test case