Support pdfs and use mini_magick
Support pdfs and use mini_magick
Merge branch 'feature/pdf-support' of github.com:jeffutter/middleman-thumbnailer into feature/pdf-support

Conflicts:
	lib/middleman-thumbnailer/extension.rb
	lib/middleman-thumbnailer/thumbnail-generator.rb
	middleman-thumbnailer.gemspec
works now
Center crop if image is different dimensions than thumbnail
Remove rogue require pry
bump mini_magick version