Report errors if sending any of the messages fails (although it never seems to).

Add verbose printing for the SET and APPLY messages.

Add newlines to some errors and verbose logs.

Refactor argument parsing to allow different kinds of scalars (not just speed).
Define brightness as a scalar type and expose a feature to set the brightness dynamically. This feature is completely necessary to operate this tool on some systems, where the brightness is reset to zero as soon as GRUB is loaded.
Does some other minor tweaking that adds little value but is generally unobjectionable.

Rewrites argument storage to handle colors and scalars with a tagged union.

Unifies an argument descriptor to set these apart in function records.

Adds default argument values and allows handlers to ignore an inapplicable argument string when a default value is set. Assigns defaults when insufficient arguments are specified.

Built-in rainbow effect now takes an optional SPEED argument.

single_breathing now sets COLOR2 and SPEED to optional. COLOR2 defaults to COLOR1. SPEED defaults to Medium.

Adds a few more color values and allows passing color names instead of hex strings.

Allows specifying Low/Medium/High for speed and brightness. Also allows argument-specific constants like slow and fast, or dim and bright.