Perf: scan and parse

instead of getting the complete list of markdown files and then parsing the markdown content later, scan and parse in the same step.

It will also allow the creation of the hierarchy and passes the Parent page along

As a bonus, the new default permalink considers the parent's permalink. It's a bit ugly but very functional

@"{%- liquid 
if page.Parent
echo page.Parent.Permalink
echo '/'
endif
if page.Title != ''
echo page.Title
else
echo page.SourceFileNameWithoutExtension
endif
-%}