Optimize build.bat and add run task

[catsuperberg]

Build.bat in it's current state doesn't delete temporary files which creates problems when working in google drive folder. It's fixable by using "del" function like this (it also doesn't output if file wasn't find which is fine):

del bin*.ilk > nul 2> nul del bin*.obj > nul 2> nul del bin*.pdb > nul 2> nul

Also it would be great if run task wouldn't build executable if source didn't change.