Open all files using encoding='utf-8-sig'

[barbieri]

Otherwise loading UTF-8 files with BOM (Byte order mark) crashes the app.

Thanks to @andreikop

Closes: #190

[coveralls]

Pull Request Test Coverage Report for Build 1888974774

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 1859076545:	0.0%
Covered Lines:	1521
Relevant Lines:	1521

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💛 - Coveralls

[andreikop]

@barbieri this version works for me