Drop six dependency

Author: boriel

tests/api/test_symbolTable.py

@@ -3,7 +3,7 @@
 
 import unittest
 from unittest import TestCase
-from six import StringIO
+from io import StringIO
 
 from src.api.symboltable import SymbolTable
 from src.api.constants import TYPE

tests/symbols/test_symbolARRAYACCESS.py

@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 from unittest import TestCase
-from six import StringIO
+from io import StringIO
 
 from src import symbols
 import src.api.global_ as gl

tests/symbols/test_symbolBINARY.py

@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 from unittest import TestCase
-from six import StringIO
+from io import StringIO
 
 from src.api.config import OPTIONS
 from src import symbols

tests/symbols/test_symbolBOUND.py

@@ -3,7 +3,7 @@
 
 import unittest
 from unittest import TestCase
-from six import StringIO
+from io import StringIO
 
 from src.api.config import OPTIONS
 from src import symbols

tests/symbols/test_symbolTYPECAST.py

@@ -1,13 +1,14 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
+
 from unittest import TestCase
+from io import StringIO
 
 from src.symbols import TYPECAST
 from src.symbols import NUMBER
 from src.symbols import VAR
 from src.symbols.type_ import Type
 from src.api.config import OPTIONS
-from six import StringIO
 from src.api.constants import CLASS
 from src.libzxbpp import zxbpp