Provide &doctest that tests Raku code contained in a Markdown file (typically a README)
&doctest's primary purpose is to run examples in READMEs and other documentation to ensure that
all examples compile and run – nothing’s worse than broken examples!
&doctest scans the Markdown file for any fenced code
blocks with 'raku' in their info
string and tests the code in each block.
If the code block has OUTPUT: «…» comments, &doctest captures the code’s output and tests it
against the expected output; if the code block doesn’t have OUTPUT comments, &doctest tests
whether the code can be EVALed ok.
&doctest also supports adding configuration info by preceding the code block with a
<!-- doctest --> comment; currently, the only config option is to provide setup code that’s run as
part of the test without being displayed in the Markdown file; in the future, this will likely
include more option, such as expecting tests to fail.