Hello.

I've been playing around with Maxima from time to time.

Ob-maxima currently does not work on Windows due to it using single 
quotes in the Maxima invocation and those not being supported by Windows 
CMD.

After some testing I've found an invocation that seems to work fine on 
both Windows and Linux. I don't think this patch can cause any real 
issue, since the string in those quotes is just the temp file path.