New parse_eon() and read_eon() parse eon strings and files into R lists.
Comments are preserved as eon_comment and eon_suffix_comment attributes.
New format_eon() and write_eon() serialize R objects to eon strings and
files. Comment attributes are emitted back into the output, so round-trips
are lossless.
New reformat_eon() normalizes indentation and spacing in an eon string
without changing data or dropping comments.
New validate_eon() returns TRUE or FALSE for whether a string is valid
eon, without throwing an error.