Reference manual polishing
Merge pull request #558 from VasylTretiakov/patch01

* patch01:
  Reference manual polishing
ConfigurationClassParser falls back to ASM-based resolution of member classes in case of NoClassDefFoundError

Issue: SPR-11844
Support for Java 8's java.util.Optional at injection points

Issue: SPR-11833
Support for java.util.Optional within ObjectFactory/Provider

Includes support for arbitrary deep nesting levels in DependencyDescriptor's getDependencyType() and MethodParameter's getNestedParameterType().

Issue: SPR-11833
Update Javadoc on SockJS client library URL

Issue: SPR-11766
Improve no content handling in MockHttpServletRequest

Issue: SPR-11764
Fix issue with RequestBody(required=true)

Issue: SPR-11828
AbstractAutowireCapableBeanFactory's getTypeForFactoryBean considers FactoryBean<Object> declarations as non-indicative (just like raw declarations)

Issue: SPR-11842