add encoding option (IDFGH-1905)

[trickre]

This commit resolve "UnicodeDecodeError" when idf.py execute.

My Environment:

• python3.7
• Windows10 pro
• Japanese

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[kumekay]

@trickre Thank you for the PR,
it was merged, with some modifications,
if solution works for you, could you please close the PR?

[Alvin1Zhang]

@trickre Thanks for contribution, changes merged with 7e5d30c, feel free to reopen.