parse the return descriptions as markdown
recurse with processMetadata for properties of the metadata
defer resolving the annotated object.

by resolving this in the exporter, we can avoid a race condtion where
sometimes relatedModule had not been indicated when it should have been.
add raw property to hold unparsed metadata
it's possible that return types might reference annotated objects
prevent property metadata overriding value metadata

this makes a property's metadata independent of the value's metadata.

fixes #61
Merge branch 'process-return-description' of git://github.com/neonstalwart/js-doc-parse
Merge branch 'property-summary' of git://github.com/neonstalwart/js-doc-parse