klippy/extras: Add boolean filter for gcode_macro.

[Luro02]

This allows one to write

{% set FLAG = params.FLAG|boolean %}

instead of

{% set FLAG = (params.FLAG|string).lowercase() == "true" %}

[KevinOConnor]

Thanks. However, I think we should try to limit the amount of Jinja2 customizations. Adding these customizations would require associated documentation (so that users knew of its existence). I agree that Jinja2 is cryptic, but I don't think we can realistically make Jinja2 "not cryptic". I fear at best we can only introduce "many different kinds of cryptic". Users today can use the standard Jinja2 documentation (which is thorough) to figure out appropriate syntax, and I think we should encourage that going forward.

Cheers,
-Kevin

[flowerysong]

% set FLAG = (params.FLAG|string).lowercase() == "true" %}

A more idiomatic way to do this is

{% set FLAG = params.FLAG | lower == "true" %}

[github-actions]

This PR is being closed because it is currently not considered a good match for the master Klipper repository.

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