import draft posts into _drafts folder

Use simple title for file, as noted on http://jekyllrb.com/docs/drafts/.
We also omit the the 'published' key in the head matter so that drafts
can be previewed using `jekyll build --drafts` without also having to
specify the --unpublished flag.
Merge pull request #147 from willnorris/drafts
Update history to reflect merge of #147 [ci skip]