Parses a YAML file into the list structure expected by poster(). Only
does light validation (presence of sections and one of layout,
grid or columns); the content builders raise their own errors for
malformed section bodies.
Value
A list following the poster() spec schema.
Examples
path <- system.file("extdata", "poster_sample.yml", package = "ggposter")
spec <- read_poster_yaml(path)