Update changelog for new release

Add explicit config for `nullable_type_declaration`

Add explicit config for `ordered_imports`

Use `is_null`

Goodbye `is_null()`, hello `null`!

Use `no_trailing_comma_in_singleline`

- Instead of deprecated `no_trailing_comma_in_list_call` and `no_trailing_comma_in_singleline_array`
- clarify readme/composer.json the config is now for v3.11 and up
- prepare for 2.1.0 release.

Use `no_trailing_comma_in_singleline`

- Instead of deprecated `no_trailing_comma_in_list_call` and `no_trailing_comma_in_singleline_array`
- clarify readme/composer.json the config is now for v3.11 and up
- prepare for 2.1.0 release.

Prepare for 2.0.0 release

Add CHANGELOG.md and bump version number

composer: any newer PHP version is good

Add README