Feature Request: Add "details" tag to whitelist

[tansaku]

I'm a little surprised that the html5 "summary" tag is whitelisted, but the "details" tag (that it is used with) is not whitelisted:

http://html5doctor.com/the-details-and-summary-elements/

Might it be possible to include the "details" tag in the white list? I think this could be a really useful feature

[jch]

Closed by #139

[mganss]

Are you sure this works as intended? I'm not a Ruby guy, but from the code it looks like you have white-listed an additional attribute, not a tag. The summary attribute that was already there is the summary attribute on the table tag.

[jch]

@tansaku @mganss ah dang it, you're right. Should've added a test for this. Would either of you be up for a follow up PR? If not, I'll get around to this in the holidays.

[jch]

Closed by #171