This commit introduces a shorthand for defining and calling macros when
using them as a reusable substitute for variables assigned complex values
(e.g. string literals with or without newline escapes). The use-case is
formatting - from my experience it's easier to visually parse a `macro`
`endmacro` block than a multiline variable assignment.

Signed-off-by: mataha <mataha@users.noreply.github.com>