Publish metalsmith custom modules

[jmatsushita]

Modified

• iilab/metalsmith-metadata : imports csv data.
• iilab/metalsmith-pandoc: Update to recent version of pandoc.
• iilab/metalsmith-search-meta: adding a pad option to create missing keys.

New

• iilab/metalsmith-generate: Generate pages from metalsmith metadata. Created for Open Mentoring.