Draft: Symfony YAML does not parse all YAML

[SOHELAHMED7]

Fixes #21

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Note

This PR remove symfony/yaml package and use php-ext-yaml instead.
php-ext-yaml does not support YAML 1.2 and symfony/yaml does.

[cebe]

I would not drop the library but rather make it possible to use both. I'd like to avoid requiring a PHP extension that is not in php core.

[SOHELAHMED7]

This will not completely solve #21.

We can 'composer suggest' consumer of this lib to use php-ext-yaml.

If the extension is present we can use or else symfony/yaml.

How do I know given YML is in which version if %YAML directive is not present?

I am asking because extension does not support YAML 1.2