Now that we have a go.mod, we can properly upgrade to blackfriday/v2
The output remains the same, but this PR brings back italic links with '_',
placing them into the link since this seems to be the more proper way.
Fixes#182
This bugfix implements correct way to calculate source sha1 hash, before it will changed,
by propagation of unchanged sources.
This commit will also include regenerated static files and *.hash files.
