add extra cost for turns in A* to avoid staircase

[reimai]

[guilhermesimoes]

Can't comment on the pull request itself, but you are using tabs when the project is using spaces for indentation. You should always follow the project's indentation style.

[qiao]

Hi @reimai, thanks for your pull request. A minor issue with your patch is that you should modify the source file located in the src directory instead of the compiled file. Then use the make command to rebuild the browser version.(You may need to install nodejs and some dependent libraries).

[ivanmayes]

Integrated this into src at #150 as well as adding some configuration for the turn penalty number.