[Feature Request] Links type to use published date metadata for external URL

[samqi]

Is your feature request related to a problem? Please describe.
I'm annoyed when Citations have Published Date that shows Date: 31 December 1969. This is due to the fact that published date is not populated, and has to be updated manually. An example of this can be found at https://foe-km.sinarproject.org/partners/foe-cluster/sinar-project/projects-2/tumpang-tanya

I can update it manually, but prefer if the code can automatically perform this action quickly.

Describe the solution you'd like
Websites with CMS of some sort, have published/modified date which can be extracted via htmldate -u . Example using sinarproject opendata page: htmldate -u https://sinarproject.org/open-government/open-data

2018-06-05

Verbose output:
htmldate -v -u https://sinarproject.org/open-government/open-data

DEBUG:urllib3.connectionpool:Starting new HTTPS connection (1): sinarproject.org:443
DEBUG:urllib3.connectionpool:https://sinarproject.org:443 "GET /open-government/open-data HTTP/1.1" 200 None
DEBUG:htmldate.core:examining meta name: <meta name="DC.date.created" content="2018-06-05T01:24:38+00:00">
DEBUG:htmldate.extractors:custom parse test: 2018-06-05T01:24:38+00:00
DEBUG:htmldate.extractors:parsing result: 2018-06-05 01:24:38+00:00

Describe alternatives you've considered
Other methods using python code can also be used..

Additional context
For advanced things like google docs or spreadsheets - a new Feature request should be created for it specifically instead with similar heading but with keyword such as Google Drive etc., cant use htmldate but more research needs to be done in a new feature request:

• I have found xmldirector (plone) as well as rclone can be considered
• other methods outlined in stackoverflow can also be considered.