add function convert date

[yechanggui]

No description provided.

[lidingpku]

this is a formal code submit, so we try our best to keep the code quality as high as possible.

please compare with existing approaches, see how many cases can be solved by those approach

• see how much work https://github.com/scrapinghub/dateparser
• https://github.com/search?l=Python&q=date+parse&type=Repositories&utf8=%E2%9C%93

if some additional features are new and not included in existing approach, see if you can combine yours and the existing approach.

the code shall be placed misc, do not create new file
https://github.com/cnschema/cdata/blob/master/cdata/misc.py

clean up your function definition
something like dateparser.parse('12/12/12')

make sure there is a clear way to handle exception, i would suggest not use try catch inside function, let user handle it would be better. otherwise, how would user know when the parser fails, and where to get error message.

testcases should be placed in tests/test_core.py