[Proposal]: Add ffmpeg creationflag in Writegear API

[abhiTronix]

Issue guidelines

• I've read the Issue Guidelines and wholeheartedly agree.

Issue Checklist

• I have searched open or closed issues and found nothing related to my idea.
• I have read the Documentation and it doesn't mention anything about my idea.
• To my best knowledge, my idea wouldn't break something for other users.

Describe your Idea

See #375 for reference
I propose a new feature to enable detached subprocess creation on Windows within the writegear module. This enhancement enhances the process management capabilities of the module.

Use Cases

See #375 for reference
This can be useful while creating an exe file for a python script that uses writegear. On windows even after creating the exe file in windowed mode or no-console mode, the ffmpeg.exe command line window would pop up while its being used by write gear.

[abhiTronix]

Successfully resolved and merged in commit 3c0dd5d