ruby : add more APIs (#2518)

* Add test for built package existence

* Add more tests for Whisper::Params

* Add more Whisper::Params attributes

* Add tests for callbacks

* Add progress and abort callback features

* [skip ci] Add prompt usage in README

* Change prompt text in example

bindings/ruby/tests/test_package.rb

@@ -8,6 +8,7 @@ class TestPackage < Test::Unit::TestCase
     Tempfile.create do |file|
       assert system("gem", "build", "whispercpp.gemspec", "--output", file.to_path.shellescape, exception: true)
       assert file.size > 0
+      assert_path_exist file.to_path
     end
   end