Add job execution limit

[tuergeist]

• Added execution limits to the jobs, execute only a certain amount of numbers, or forever (default)
• Added optional initial delay, if the first execution shall be done immediately or with a higher/lower delay as the interval, this option can be used
• updated the README accordingly
• version bump

[glensc]

this seems to be in timeloop-ng fork:

• https://github.com/tuergeist/timeloop

but it also seems dead?

• tuergeist@d28d9fa#r140157788