CrontabParser: Tag specials in the special rule

For consistency with the schedule rule and to make testing easier.
CrontabParser: Spec test the schedule parsers

Added some spec tests that cover the parsing of normal and special schedules.
There are already some failuers as the parsers are currently matching 0 or more
characters in places where 1 or more is required.
CrontabParser: Fix repeats in schedule parsing

The schedule parsers were requiring whitespace and non-whitespace sequences to
repeat _0_ or more times. This commit fixes those repetitions to be _1_ or more
times.