No code modification.
PHPDoc signature update: added throws an InvalidArgumentException.

Don't override the timezone when called with a DateTime object

Fix fatal error when using the default PHP locale #17

Thanks to @jonasraoni

Fix fatal error with non-Gregorian locales (#15)

Thanks to @asmecher

Account for different handling of historical dates by ICU and Posix #5
Minimum PHP version in composer.json is incorrect #6

Thanks to @IMSoP

Added documentation of formats
Added test for all formats
Fixed some formats

Automatic run PHPUnit tests with Actions.

composer run-script test

Catch exception thrown when creating DateTime object with invalid $timestamp value.