Pyccolo

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* Allow per-handler reentrancy;

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* Add eval helper;
* Add syntactic macro examples (quasiquotes and quick lambdas);
* Add support for conditional handlers;

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* Add cli;
* Add basic readme documentation;
* Allow returning pyc.Skip for skipping subsequent handlers for same event;
* Misc improvements to file filter hooks;
* Allow returning lambdas for before_expr events;

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* Misc ergonomics improvements;
* Enable for Python 3.10;
* Enable linting and fix package-level imports;

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* Get rid of future-annotations dependency;
* Fix memory leak in sandbox exec;

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* Misc composability improvements and fixes;
* Improve file filter handling;