change config specifiers in input file format

Instead of a dictionary/object, input file options are now specified
by a 'key=value' pair starting with '-' for options only applying to
the next URL or '-G' for Global options applying to all following URLs.

See the docstring of parse_inputfile() for details.

Example option specifiers:

- filename = "{id}.{extension}"
- extractor.pixiv.user.directory = ["Pixiv Users", "{user[id]}"]
-spaces="are_optional"
-G keywords = {"global": "option"}

gallery_dl/util.py

@@ -261,10 +261,9 @@ class ChainPredicate():
 
 
 class ExtendedUrl():
-    """URL with attached config dict"""
-    def __init__(self, url, confdict):
-        self.value = url
-        self.config = confdict
+    """URL with attached config key-value pairs"""
+    def __init__(self, url, gconf, lconf):
+        self.value, self.gconfig, self.lconfig = url, gconf, lconf
 
     def __str__(self):
         return self.value