reported number of "current features" for ldf examples

This solves two of the three problems observed in issue #439 
*  "current features" now include all lines of an ldf example (not just the first line)
*  "current features" now include also "shared" features in ldf examples

It does not solve the third problem which quite hard for me
* "current features" don't include --quadratic and --cubic features where one namespace is "shared",
beacuse VW::setup_example is called before the namespaces from "shared" are added via add_example_namespaces_from_example.