#14 move frontmatter into separate template, fix frontmatter

examples/docs/abstract.schema.md

examples/docs/definitions.schema.md

examples/docs/example.schema.md

examples/docs/simple.schema.md

examples/docs/subdir/subdir.schema.md

lib/markdownWriter.js

package.json

templates/md/divider.ejs

templates/md/header.ejs