Negative numbers for @ are not being recognized

[philolo1]

While "@0" and "@positive" integer work, "@-1" does not work.

On GNU date it returns the time in seconds before JAN 01 1970.

For example:

"date -d '@-1'"     
Thu Jan  1 08:59:59 JST 1970

"date -d '@-1000000'"           
Sat Dec 20 19:13:20 JST 1969

[philolo1]

I would suggest we also use nom for this and extract part of the code that currently handles "@" and create a new file parse_timestamp to make the code more readable.
@sylvestre @tertsdiepraam