UPGRADE FROM 3.x to 4.0

DependencyInjection

Using unsupported configuration keys in YAML configuration files raises an exception.
Using unsupported options to configure service aliases raises an exception.

The choices_as_values option of the ChoiceType has been removed.
Support for data objects that implements both Traversable and ArrayAccess in ResizeFormListener::preSubmit method has been removed.

Possibility to pass objects as URI attributes to the ESI and SSI renderers has been removed. The inline fragment renderer should be used with object attributes.

The ability to pass a Doctrine Cache instance to the ClassMetadataFactory class has been removed. You should use the CacheClassMetadataFactory class instead.

Starting an unquoted string with % leads to a ParseException.
The Dumper::setIndentation() method was removed. Pass the indentation level to the constructor instead.
Removed support for passing true/false as the second argument to the parse() method to trigger exceptions when an invalid type was passed.

Before:
```
Yaml::parse('{ "foo": "bar", "fiz": "cat" }', true);
```
After:
```
Yaml::parse('{ "foo": "bar", "fiz": "cat" }', Yaml::PARSE_EXCEPTION_ON_INVALID_TYPE);
```

Removed support for passing true/false as the third argument to the parse() method to toggle object support.

Before:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', false, true);

After:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', Yaml::PARSE_OBJECT);

Removed support for passing true/false as the fourth argument to the parse() method to parse objects as maps.

Before:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', false, false, true);

After:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', Yaml::PARSE_OBJECT_FOR_MAP);

Removed support for passing true/false as the fourth argument to the dump() method to trigger exceptions when an invalid type was passed.

Before:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, true);

After:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, Yaml::DUMP_EXCEPTION_ON_INVALID_TYPE);

Removed support for passing true/false as the fifth argument to the dump() method to toggle object support.

Before:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, false, true);

After:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, false, Yaml::DUMP_OBJECT);

The !!php/object tag to indicate dumped PHP objects was removed in favor of the !php/object tag.