#25539 - Rename has_breadcrumb to simple_breadcrumbs

This pull request renames the has_breadcrumb gem to simple_breadcrumbs due to the name has_breadcrumb not being available on rubygems.org.

The only items changed are the .gemspec and the README.  The .gemspec has had its meta data updated to identify the gem as simple_breadcrumbs.  The README required updating the installation instructions and removing references to has_breadcrumb.

[#25539](https://squaremouth.lighthouseapp.com/projects/63460-viper/tickets/25539-rename-has_breadcrumb-to-simple_breadcrumbs)