Don't fail on unknown types while checking yaml files.

Fixes first comment in #219 (seems that Github doesn't allow referencing commencts in commit messages...)
Catch both ScannerError and ParserError while loading yamls

- Also, don't print out warning messages when building cache, they'd be shown twice to user.
Fixes #219
Fixed documentation for ask_confirm
Merge pull request #224 from phracek/master

Fix issue #200