cancel running jobs if possible when run Scheduler.StopJobs()

[27149chen]

What does this do?

when run Scheduler.StopJobs(), the scheduler will wait for the running jobs to be completed. If there are long running jobs, it will always return "timed out waiting for jobs to finish".

This pr try to cancel the running jobs if possible

Which issue(s) does this PR fix/relate to?

Resolves #818

List any changes that modify/break current functionality

You can now add a task function which accept ctx as the first param, but you do need pass a ctx actually, gocron will handle it properly

	j, err := s.NewJob(
		gocron.DurationJob(
			10*time.Second,
		),
		gocron.NewTask(
			func(ctx context.Context) {
				// do things
			},
		),
	)

but if you have you own ctx, fell free to pass it

	j, err := s.NewJob(
		gocron.DurationJob(
			10*time.Second,
		),
		gocron.NewTask(
			func(ctx context.Context) {
				// do things
			},
                         ctx,
		),
	)

or you can also pass it as a job option to control the whole thing

	j, err := s.NewJob(
		gocron.DurationJob(
			10*time.Second,
		),
		gocron.NewTask(
			func(ctx context.Context) {
				// do things
			},
		),
                gocron.WithContext(ctx)
	)

Have you included tests for your changes?

yes

Did you document any new/modified functionality?

• Updated example_test.go
• Updated README.md

Notes

[JohnRoesler]

Hey @27149chen this is a great addition. Some things that will be needed still:

• addition of the new method to example_test.go
• additional comments on the NewJob and NewTask functions explaining that if your task accepts a context as it's first parameter, gocron will pass in a context you can listen to for cancellation. Also, updating the example_test.go for the NewTask

I will make a PR to address.