DATAREST-130 - Support nulling out properties when doing HTTP PUTs.
DATAREST-130 - Code polish and JavaDoc.
DATAREST-130 - Added test case for DomainObjectMerger.
DATAREST-130 - Polished test implementation.

JavaDoc, formatting, simplified implementation.
DATAREST-107 - Respect @RestResource exported flag on query methods.

ResourceMappings now only adds a RepositoryMethodResourceMapping if it's really exported.
DATAREST-107 - Add tests to verify ambiguous mapping detection.
DATAREST-107 - Polishing test cases.

Extracted DATAREST-107 specific test cases into separate test method.
DATAREST-220 - Added contribution guidelines.

Linked to the actual contribution guidelines maintained in the Spring Data Build project.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/DomainObjectMerger.java
	spring-data-rest-core/src/test/java/org/springframework/data/rest/core/support/DomainObjectMergerTests.java