To automate EXPORT_OK list construction.
yatt:foreach nth=i -- for builtin loop counter, starting from 1.
Minor breakpoint cleansing.
More for #19 - Test updates and better hashparam utils.

* `YATT::Lite::Util::att_value_in($params, $type, $name, $formal_value, $as_value)`
* Partial::Session param() assignment behavior is slightly changed.
ytmpl/error.ytmpl - for detailed backtrace, ported from Devel::StackTrace::AsHTML