Fix utils.py for PyPy on Windows

The line
```python
from __future__ import unicode_literals
```
introduced in commit [ecc0c5ee01](ecc0c5ee01) broke youtube-dl for PyPy on Windows, making it unable to locate WinAPI functions.
Error: "TypeError: function name must be a string or integer"

Adding "b" prefix to strings with WinAPI function names fixes it.

youtube_dl/utils.py

@@ -808,22 +808,22 @@ def _windows_write_string(s, out):
 
     GetStdHandle = ctypes.WINFUNCTYPE(
         ctypes.wintypes.HANDLE, ctypes.wintypes.DWORD)(
-        ("GetStdHandle", ctypes.windll.kernel32))
+        (b"GetStdHandle", ctypes.windll.kernel32))
     h = GetStdHandle(WIN_OUTPUT_IDS[fileno])
 
     WriteConsoleW = ctypes.WINFUNCTYPE(
         ctypes.wintypes.BOOL, ctypes.wintypes.HANDLE, ctypes.wintypes.LPWSTR,
         ctypes.wintypes.DWORD, ctypes.POINTER(ctypes.wintypes.DWORD),
-        ctypes.wintypes.LPVOID)(("WriteConsoleW", ctypes.windll.kernel32))
+        ctypes.wintypes.LPVOID)((b"WriteConsoleW", ctypes.windll.kernel32))
     written = ctypes.wintypes.DWORD(0)
 
-    GetFileType = ctypes.WINFUNCTYPE(ctypes.wintypes.DWORD, ctypes.wintypes.DWORD)(("GetFileType", ctypes.windll.kernel32))
+    GetFileType = ctypes.WINFUNCTYPE(ctypes.wintypes.DWORD, ctypes.wintypes.DWORD)((b"GetFileType", ctypes.windll.kernel32))
     FILE_TYPE_CHAR = 0x0002
     FILE_TYPE_REMOTE = 0x8000
     GetConsoleMode = ctypes.WINFUNCTYPE(
         ctypes.wintypes.BOOL, ctypes.wintypes.HANDLE,
         ctypes.POINTER(ctypes.wintypes.DWORD))(
-        ("GetConsoleMode", ctypes.windll.kernel32))
+        (b"GetConsoleMode", ctypes.windll.kernel32))
     INVALID_HANDLE_VALUE = ctypes.wintypes.DWORD(-1).value
 
     def not_a_console(handle):