File.exists? is now deprecated in Ruby, use File.exist? instead

https://github.com/ruby/ruby/blob/trunk/file.c#L1462
Merge pull request #121 from rsempe/master

File.exists? is now deprecated in Ruby, use File.exist? instead
Use Rails root
Merge pull request #122 from dtaniwaki/use-rails-root

Use Rails root
Don't do substitutions if the variable is single quoted.
Merge pull request #124 from ericroberts/single-quoted-variables

Don't do substitutions if the variable is single quoted.
Call the right method in the spec

closes #129
Don't encourage use of yaml syntax
docs
Use comment instead of "protected" to denote internal method
Avoid using #inject

I did not use #each_with_object, as the Rogues recommend, for two reasons:

1. I find it just as confusing as #inject.
2. Dotenv still technically supports Ruby 1.8
Doc what is returned from Dotenv.with
Link to Ruby Rogues code reading
Merge pull request #130 from bkeepers/ruby-rogues-feedback

Ruby Rogues feedback
Update README.md
Update README.md
Merge pull request #132 from coderly/add-newline-support-to-readme

Add newline support to readme
update changelog
extend self instead of defining class methods
extend self instead of defining class methods