ruby : output format (#3237)
* Fix a typo
* Don't allocate output string unless needed
* Add methods to output SRT and WebVTT
* Add tests for output methods
* Make constants for output private
* Add signatures for output methods
* Add document on output methods
* Fix method name: Segment#speaker_next_turn? -> #speacker_turn_next?
* Add Whisper::Segment#descotruct_keys
* Add test for Whisper::Context#descotruct_keys
* Add signature of Whisper::Segment#deconstruct_keys
* Use parentheses to suppress warning
* Update date
fbead67549