silence removal for transcription implemented

[artshcherbina]

Thank you for you great work!

I've added some simple logic to detect silence, and process only real voice input.
I start transcription, if more then 1 second of silence is passed (You may need to tune --pressure-t to your microphone).
You may tune silence duration with --silence_t argument.
Transcribed text is copied to the clipboard (currenly only on linux, xclip is used).
The code can be further improved, if it seems reasonable.

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9---------
99---------
99---------
3992---------
93992---------
93999---------
994999---------
9994999---------
69992994---------
769992994---------
9-9995999---------
-9-9996999---------
--9-9996999---------
--795999-995---------
---694999-995---------
----694999-996---------
-----929998999---------
------929999899---------
-------929999799---------
-------593999-998---------
--------493999-999---------
---------929999699---------
 Here is some English text
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6---------
96---------
99---------
999---------
2997---------
9-997---------
99-997---------
7999992---------
-6998992---------
9-6998992---------
92-992998---------
492-993999---------
799-5997993---------
6799-5997993---------
59492-994999---------
459493-995999---------
4459493-995999---------
-755899-4995994---------
2-755889-4995994---------
-2-755989-4995994---------
--33559594-997999---------
---33559594-998999---------
---22754979-3994995---------
----22754979-3993995---------
------2754969-3993995---------
------32659596-999999---------
-------32658596-999999---------
--------32658696-899999---------
---------3744959-2992996---------
 During silence nothing is detected.
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