chore: git subtree for deps

[hi-ogawa]

Since diff is becoming huge, patch is not really appropriate at this point.
Also, it would be too tedious to fork all of these repositories.
First time trying git subtree, but it looks reasonable use cases here.

git subtree add --prefix subtree/cachelib   https://github.com/s3bk/cachelib     master --squash
git subtree add --prefix subtree/pdf_fonts  https://github.com/s3bk/pdf_fonts    master --squash
git subtree add --prefix subtree/pdf        https://github.com/pdf-rs/pdf        master --squash
git subtree add --prefix subtree/pdf_render https://github.com/pdf-rs/pdf_render master --squash

todo

• cargo fmt
• apply patches feat: patch deps #5

reference

• https://www.atlassian.com/git/tutorials/git-subtree