Implementation of custom object id resolution.
Fix deserialization of null values for collection/array type deserializers
* All of these deserializers should ask the encapsulated valueDeserializer for its nullValue when `VALUE_NULL` is encountered, rather than assuming a return value of `null`.
* This is a bug that affects the ser/deser of `Collection[Option[_]]` in scala, as `None` values are serialized to `null` and deserialized back to `null` rather than `None`, which is correctly overriden in `OptionDeserializer`
* Note I am a first time committer and happy to sign any release. Thanks!
tests for custom null deser with collections
unit tests showing custom null deserialization of values in arrays and maps
Merge branch 'custom-id-resolution' of https://github.com/pgelinas/jackson-databind into pgelinas-custom-id-resolution

Conflicts:
	src/main/java/com/fasterxml/jackson/databind/deser/BeanDeserializerBase.java
Merge pull request #407 from wpalmeri/null-deser-cleanup

Fix deser of null values for collection/array type deserializers
Add notes regarding #407
Fix #411 for master
Fix a prob b/w positive/negative inf parsing
Add a (failing) unit test for #412
Fix #412 in master
Minor improvement to earlier #412 fix
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warnings cleanup
Fix #420 also for master
Minor improvement to handling of JsonGenerator.close() on exception case
update dep
update release notes
Update CalendarSerializer.java

// _customFormat cannot parse Calendar, so Date should be passed
Improve unit testing for trees vs polymorphic