fix(api): declare __all__ and export UndefinedLiteral - #83

Unexpected input(s) 'enable-caching', valid inputs are ['version', 'version-file', 'python-version', 'activate-environment', 'venv-path', 'working-directory', 'checksum', 'github-token', 'enable-cache', 'cache-dependency-glob', 'restore-cache', 'save-cache', 'cache-suffix', 'cache-local-path', 'prune-cache', 'cache-python', 'ignore-nothing-to-cache', 'ignore-empty-workdir', 'tool-dir', 'tool-bin-dir', 'manifest-file', 'add-problem-matchers', 'resolution-strategy']

Unexpected input(s) 'enable-caching', valid inputs are ['version', 'version-file', 'python-version', 'activate-environment', 'venv-path', 'working-directory', 'checksum', 'github-token', 'enable-cache', 'cache-dependency-glob', 'restore-cache', 'save-cache', 'cache-suffix', 'cache-local-path', 'prune-cache', 'cache-python', 'ignore-nothing-to-cache', 'ignore-empty-workdir', 'tool-dir', 'tool-bin-dir', 'manifest-file', 'add-problem-matchers', 'resolution-strategy']