temporary directory clean up

[rolfn]

The current version of "node-latex" uses version 0.5.x of the module "temp". This version automatically removed the tempory directory at exit (maybe your explicit remove calls aren't necessary?). Sometimes for debugging it would be helpful if the temporary directory is not deleted at the end. I suggest an additional parameter "keep" for the options object which defaults to false. In the current version of "temp" "track()" or "cleanup()" must be called explicitly for clean up. Thanks.

...Rolf

[mikolalysenko]

This seems like a reasonable thing. If you want to take a crack at fixing it, I would accept a pull request.