Add support for environment variables in rewrite (#281)

* Added support for environment variables in rewrites

* Restricted shell expansion to environment variables

🐛 fix: 0.8.5: Log useful errors when unable to bind mount a rewrite o…

…nto a target

Merge branch 'mistress' of github.com:queer/boxxy into mistress

🔨 chore: 0.8.3: I am stupid and missed updating Cargo.toml

✨ feature: 0.8.2: Explain AppImage errors where possible

✨ feature: 0.8.1: Reduced log noise, updated deps

✨ feature: 0.8.1: Reduced log noise, updated deps

✨ feature: 0.8.0: --no-config, --rule (closes #70)

chore: Release boxxy version 0.7.2

chore: Release boxxy version 0.7.1