@default tag: added support for object literal defaults

Default object literals are now stored as a string. In the default
template they are shown with syntax highlighting.
@default tag with object literals

Changed boolean 'doclet.defaultobject' to 'doclet.defaultvaluetype' field. Improved unit testing and fixed template.
Merge pull request #419 from ErnstHaagsman/default-tag-objects

@default tag: added support for object literal defaults