* Add a basic Crawler.crawl_async().
* Add custom loop tests for *CrawlerRunner.
* Add AsyncCrawlerProcess.
* Update related docs.
* Update practices.rst.
* Address test failures.
* Add a note about AsyncCrawler* to the docs about switching reactors.
* Address feedback.
* Update for TID253.
* Simplify test_crawler_crawl_async_twice_parallel_unsupported().
* Enable AsyncioSelectorReactor by default.
* Improve get_crawler(), switch more tests to it.
* Fix the remaining default-reactor test failures.
* Address documentation feedback.
* Make pinned envs more consistent.
Change python code snippets to begin with '.. code-block:: python' to be recognized by the hook for formatting. All snippets under '::' (rst literal blocks) are ignored.