hugolib: markdown_title: add title from markdown

hugolib: markdown_title: add title from markdown

Getting title from the page itself, as first encountered header in
markdown file.

Currently it's inefficient as we parsing page twice, the first in some
ealier point when hugo renders markdown, so it should be embedded
somewhere in that place.

But currently i don't care about if a PoC implementation.

Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>