Add a Rakefile and Gemfile

- Add a Rakefile with the 'new_post' task
- Add a Gemfile with the 'stringex' gem (for the 'to_url' method)
Check for nil in get_stdin
Replace 'answer' with 'response'
Add a space after the message given to get_stdin()

Specifically, add a space after the message when ask() is called
without any options.
Don't allow empty or nil responses
Revise text in command-line output
Don't create the posts directory immediately

Wait until we are certain that the user wants to create the new blog
post.
Add a blank line after the user's response
Use UTC as the time zone for site generation