Add support for comments

Some Wordpress posts use <!--more--> to specify where the excerpt should stop. This commit preserves those comments.
filter file attachments from exported posts
Merge pull request #13 from bensheldon/ignore_attachments

Filter file attachments from exported posts
Merge pull request #15 from monfresh/add-support-for-comments

Add support for comments
Merge branch 'master' into to_yaml_for_frontmatter

Conflicts:
	spec/lib/wp2middleman/migrator_spec.rb