fix(expression_extractor): correctly support @ mapping spec, remove old specs
feat(compiler): allow specifying attribute mappings using annotations

Closes #227
chore(release): v0.9.1
feat(scope): add support to skip auto digest in a turn

Closes #235
chore(sdk): remove uses of meta package
chore(import): make all imports package:canonical
chore(cla): added cla signers
fix(syntax): warnings in directive code