added ArrayNodeDefinition::canBeEnabled() and ArrayNodeDefinition::canBeDisabled()
to ease configuration when some sections are respectively disabled / enabled
by default.
added a normalizeKeys() method for array nodes (to avoid key normalization)
added numerical type handling for config definitions
added convenience methods for optional configuration sections to ArrayNodeDefinition
added a utils class for XML manipulations
2.1.0
added a way to add documentation on configuration
implemented Serializable on resources
LoaderResolverInterface is now used instead of LoaderResolver for type
hinting
