Commit 6714ac6 broke Windows compatibility

[glumia]

Commit 6714ac6 broke windows compatibility.
If the user gives a folder as third argument the script should check what's the environment and then eventually add a '\' if we are on Windows and a '/' if we are on Unix.

Example output:

C:\Users\gius\Desktop\openload-dl-master>python openload-dl "https://oload.fun/f/5HHWrGijP7U/Naruto_001.mp4" C:\User\gius\Desktop
Extracting download link for C:\User\gius\Desktop/Naruto 001.mp4
Download of C:\User\gius\Desktop/Naruto 001.mp4 in progress...
Traceback (most recent call last):
  File "openload-dl", line 74, in <module>
    with open(filename,'wb') as fp:
FileNotFoundError: [Errno 2] No such file or directory: 'C:\\User\\gius\\Desktop/Naruto 001.mp4'

[glumia]

Solved with commit 7db3800.
If the user wants to download the file in a particular folder he can specify the full path with '-o' option.