Support for multiline entries

[RaphMad]

While migrating some of my cronjobs to supercronic, I noticed that multiple lines joined together with the \ character work in cron, but are not supported in supercronic.

For example:

*/10 * * * * echo 'a' && \
                  echo 'b' && \
                  echo 'c'

Is a valid crontab entry for most classic crons, but is rejected by supercronics parser.

[neurosnap]

Greetings! Thanks for submitting this issue. I'd be happy to accept a PR (with tests) to support this feature.