New Project Template improvements

[hmans]

Things we should add to the new project template:

• a binstub for flutterby
• change date of generated blog post to today
• an RSS feed for the blog section
• an index for the blog section
• change templates to ERB, not Slim, in preparation for removing Slim as a Flutterby dependency
• add a sample Rakefile with a deploy task (and a bin/rake binstub)