Squashed 'libertree-frontend-ramaze/' changes from fdcbc88..20324b2

20324b2 update libertree-model

git-subtree-dir: libertree-frontend-ramaze
git-subtree-split: 20324b24024835081aaa76b81cd647916468174a
Merge commit 'ff6403e4bb5e407c789b679d8d0f7a090476d07d'
Squashed 'libertree-backend-rb/' changes from f85b38a..115e3b9

115e3b9 update libertree-model

git-subtree-dir: libertree-backend-rb
git-subtree-split: 115e3b99ccd880e1d0fd1593b352e906438ee015
Merge commit 'edc0b92f53ab91d7bfdb8c8f7b2daf896a6284fa'
Squashed 'libertree-model-rb/' changes from 148a6c0..7e218af

7e218af bump gem version
8f86b30 explicitly require 'set'

git-subtree-dir: libertree-model-rb
git-subtree-split: 7e218afbb9084410174a904faa414f5880184f52
Merge commit '9eaa6511f7cbbb80cc6224c7cc128413c51713bd'