Configure files and executable in gemspec
Add Rakefile with package task

See Build Awesome COmmand-Line Applications in Ruby pg 104
Gem::PackageTask instead of Rake::GemPackageTask

Fixes ERROR: 'rake/gempackagetask' is obsolete and no longer supported. Use
'rubygems/package_task' instead.
http://apidock.com/ruby/Gem/PackageTask
Bug fixes in gemspec
Add homepage and description to spec

Avoids warnings from `gem build`