Composer 2 support

• add support for Composer 2
• fix incorrect return type for the command
• fix typos
• update README

Change package name

The package name is now beapi/composer-freeze-version.

force string for packages

1.0.2

force string package

Lower php requirements

1.0.1

Lower PHP requirements to PHP 5.6

composer package

1.0

Update README.md