Squashed 'libertree-model-rb/' changes from 6797648..e840d12

e840d12 use published version of parkdown

git-subtree-dir: libertree-model-rb
git-subtree-split: e840d12e5e88da5c47f064cd856ee9c311496c9c
Merge commit '11ef7f159399f137b2f75aea1fe789e7733cb268'