Add debug message for date parsing error
Refactoring: classmethod to plain method
Fix the incorrect Wretch date like 2/30, 2/31 =.=
iconv big5 -> utf8

What the hell was I think 6 yrs ago? Using big5 in the source code?
FIX: Article-comment incorrect relationship.

Before fixing this issue:
- If the first article is unselected and it has comments, an exception
  will be raised.
- If some article with comment is unselected, the comments will belong
  to incorrect article