Add AttachmentToHTML::Adapters::PDF
Add AttachmentToHTML::Adapters::RTF
Use Nokogiri in AttachmentToHTML specs
Test AttachmentToHTML::Adapters for success
Accept options to AttachmentToHTML#to_html
Raise exception for missing AttachmentToHTML adapters
WIP add AttachmentToHTML
Add AttachmentToHTML::HTML class to store results

Rather than just returning a string which gives us no metadata, return a HTML instance so that we can query it for things like #success?