Move one function to util.py
Totally rewrite bddown_core

Found a new way to parse html to get what we need.
And it support multi-file download(not the folder).
(link like that: http://pan.baidu.com/s/1hqfymMS)
Move download to command/
Fix unicode escape
Clean up
Support folder download

Still need more tests about it.
Fix import error
Fix a little bug
Update README
Handle bdstoken

If ``bdstoken`` is null, an error may occur.

This solution is not perfect and need more test.
Code encodings
Parse url to support more future features
Support album download
Update README