Reifying the notion of a schedule helps reasoning about the code.
Passing a schedule as an argument to related procedures allows writing
simpler unit tests.
* src/mcron/base.scm(<schedule>): New record data type.
(make-schedule, schedule-user, set-schedule-user!)
(schedule-system, set-schedule-system!)
(schedule-current, set-schedule-current!): New procedures.
(system-job-list, user-job-list, configuration-source): Replace those
global variables with ...
(%global-schedule): ... this global <schedule> instance.
* src/mcron/base.scm (use-system-job-list, use-user-job-list)
(remove-user-jobs, clear-system-jobs, add-job, find-next-jobs)
(display-schedule, run-job-loop): Add '#:SCHEDULE' keyword argument.
* doc/mcron.texi (The base module): Update documentation.
ac39c00859