Translate library/urllib.request.po
This one is relatively big, is it ok to translate all the contents in one PR or should I separate into several PRs?

Progress:

• urllib.request 的 functions
• urllib.request 的 classes (part 1, until urllib.request.Request)
• urllib.request 的 classes (part 2, all other classes) (WIP)
• Request Objects
• OpenerDirector 物件
• BaseHandler 物件
• HTTPRedirectHandler 物件、HTTPCookieProcessor 物件、ProxyHandler 物件
• HTTPPasswordMgr 物件、HTTPPasswordMgrWithPriorAuth 物件
• AbstractBasicAuthHandler 物件、HTTPBasicAuthHandler 物件、ProxyBasicAuthHandler 物件
• AbstractDigestAuthHandler 物件、HTTPDigestAuthHandler 物件、ProxyDigestAuthHandler 物件
• HTTPHandler 物件、HTTPSHandler 物件、FileHandler 物件、DataHandler 物件、FTPHandler 物件
• CacheFTPHandler 物件、UnknownHandler 物件、HTTPErrorProcessor 物件
• Examples
• Legacy interface
• urllib.request Restrictions
• urllib.response --- Response classes used by urllib