Parametrize-from-file

Documentation

* docs: fix typos ([`38cea18`](https://github.com/kalekundert/parametrize_from_file/commit/38cea1863d62ec1202dfc94ed730e099c38e7bb8))

* docs: fix python snippet examples ([`5497205`](https://github.com/kalekundert/parametrize_from_file/commit/5497205cd718d4898659f4924fd81a139b1b2d4e))

Feature

* feat: add empty_ok() for voluptuous schema ([`6fd446d`](https://github.com/kalekundert/parametrize_from_file/commit/6fd446dd8017f38cfff02beec6c0e1d7a90e2379))

Feature

* feat: get multiple variables from executed snippets ([`c43c57a`](https://github.com/kalekundert/parametrize_from_file/commit/c43c57af9045586f5ab81f9cd3c86bb523d6c60b))

Fix

* fix: improve debug message ([`08fa038`](https://github.com/kalekundert/parametrize_from_file/commit/08fa0382d20bbc73312f11232105fa5a1f325357))

Feature

* feat: try to import the voluptuous submodule ([`4d5cca4`](https://github.com/kalekundert/parametrize_from_file/commit/4d5cca4581b82526acd1174d66256281b48d9185))

Feature

* feat: allow exec() and eval() to be deferred

This commit also gets rid of exec_and_lookup(), which was basically just
doing one specific kind of deferral. Fixes 8. ([`b8cf9d5`](https://github.com/kalekundert/parametrize_from_file/commit/b8cf9d5a10fa9389fb4f90980cce5cc48b30a5b0))

* feat: make namespaces immutable, add more error checks

- Make namespaces immutable, fix 10.
- Provide more flexible exception assertions, fix 9.
- Add sensible `__bool__()` implementation for error context managers,
fix 12. ([`8e52066`](https://github.com/kalekundert/parametrize_from_file/commit/8e52066babd80bee0ca3ff2786ddb325ad16110e))

Test

* test: make sure namespaces with unpickleable values can be copied ([`1c61ee8`](https://github.com/kalekundert/parametrize_from_file/commit/1c61ee873e8abc90b052adf309f275b58950dabd))

Fix

* fix: include voluptuous dependency ([`62fc60b`](https://github.com/kalekundert/parametrize_from_file/commit/62fc60ba8e1dfe0ab93a8f96b9e3b8e2dca1292d))