Rework the parser so we can use arbitrary start nodes of the syntax.

This also includes a rework for error recovery in the parser. This is now just possible for file_input parsing, which means for full files.
Includes also a refactoring of the tokenizer. No more do we have to add an additional newline, because it now works correctly (removes certain confusion.

jedi/parser/pgen2/parse.py

@@ -60,7 +60,7 @@ class PgenParser(object):
 
     """
 
-    def __init__(self, grammar, convert_node, convert_leaf, error_recovery):
+    def __init__(self, grammar, convert_node, convert_leaf, error_recovery, start):
         """Constructor.
 
         The grammar argument is a grammar.Grammar instance; see the
@@ -90,8 +90,6 @@ class PgenParser(object):
         self.convert_node = convert_node
         self.convert_leaf = convert_leaf
 
-        # Prepare for parsing.
-        start = self.grammar.start
         # Each stack entry is a tuple: (dfa, state, node).
         # A node is a tuple: (type, children),
         # where children is a list of nodes or None