Updated to Rspec 3.
Replace deprecated File.exists? method with File.exist?
Remove "require 'spec/autorun' from spec_helper.rb to get rid of a deprecation warning.
Added SVG file for the main icon to the vendor directory.

It may come handy to get the icon at different resolutions with minimal degradation in the future.
Recreated the 18x18 px version of the main icon from the full-sized SVG file.

It looks better than the previous version, which was a resized PNG file.
Renamed "spec_helper.rb" to "rails_helper.rb" as a preliminary to follow the rspec-rails 3 upgrade procedure:

https://github.com/rspec/rspec-rails#upgrading-an-existing-app
Auto-generated spec_helper.rb file and incoporated suggested changes in rails_helper.rb

This brings rspec config in line with rspec and rspec-rails 3 best practices. See:

https://github.com/rspec/rspec-rails#upgrading-an-existing-app
WIP: Change deprecated rspec :should syntax to new :expect syntax.
Fix tests.
Explicitly require rspec/core in spec_helper.rb. Otherwise Rubymine gets confused and cannot run tests.

Definitely a bug in Rubymine, but easy to work around.
Removed rspec-expectations specific config.

Both "should" and "expect" syntaxes are enabled by default. This suits me for now, no need to change the defaults.
Remove old "stub" syntax, use new rspec 3 "allow" syntax instead.
Changed tests to the new rspec 3 "allow" and "expect" syntax, instead of "stub" and "should".

This has been mostly automated with the Transpec gem. For more about Transpec see:

http://yujinakayama.me/transpec/
Fix tests.
Fix tests.