buddhist_datetime_dateformat_sns 1.0.7

fork of https://github.com/teerasej/dart-flutter-buddhist-datetime-dateformat to support sound null safety

[1.0.6] - 05/06/2020.

• fix link to Thai manual, finally

[1.0.5] - 05/06/2020.

• fix link to Thai manual

[1.0.4] - 05/06/2020.

• Add example photo in README.md

[1.0.3] - 05/06/2020.

• fix miscalculation in DateFormat

[1.0.2] - 05/06/2020.

• Add "How to use"
• Add "How to use" in Thai

[1.0.1] - 05/06/2020.

• Formatted code
• add example

[1.0.0] - 05/06/2020.

• Add extension for DateFormat with Thai's Buddhist calendar support (ค.ศ. เป็น พ.ศ.).
• Add extension for DateTime that can get year by converted into Buddhist calendar's value.