[Windows] Writes corrupted image

[Reawel]

Hey Arafatk,
when using this library under Windows, it saves the .png file in silence, but the file cannot open.
The problem is that Gnuplot under windows has a problem with the '\' in the filepaths

I could fix this problem with a quick and dirty replacing all '\' with '/'

Just FYI.

PS: Nice library, though.

[arafatkatze]

@Reawel That fix would be awesome thanks a lot