Replace non filename compatible chars in fields

Values that got inserted in dirname and filename pattern get cleared
from characters that will not work in filenames.
This is also helpful for #262.

instaloader/instaloader.py

@@ -111,6 +111,16 @@ class _PostPathFormatter(_ArbitraryItemFormatter):
             ret = ret.replace('\\', '\ufe68').replace('|', '\uff5c').replace('?', '\ufe16').replace('*', '\uff0a')
         return ret
 
+    def get_value(self, key, args, kwargs):
+        """Replaces '/' with similar looking Division Slash and on windows newline with space"""
+        ret = super().get_value(key, args, kwargs)
+        if not isinstance(ret, str):
+            return ret
+        ret = ret.replace('/', '\u2215')
+        if platform.system() == 'Windows':
+            ret = ret.replace('\n', ' ')
+        return ret
+
 
 class Instaloader:
     """Instaloader Class.