add examples for all funcs, license tweak, func name clarifications

[JohnRoesler]

What does this do?

• adds examples for all functions
• removes all examples from the readme
• renames a few functions and changes some signatures
• moves the license to an MIT license (almost the same wording) - gets a nice standard license

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

resolves #95

List any changes that modify/break current functionality

• The job Tag func now accepts a variadic string parameter instead of a slice
• The scheduler SetTag is now Tag and also accepts a variadic string parameter
• The scheduler RemoveJobByTag is now RemoveByTag to be consistent with Remove and RemoveByReference
• The scheduler RunAllWithDelay func now accepts a time.Duration instead of an int representing seconds
• The scheduler Scheduled func is now TaskPresent - scheduled was confusing name because until the scheduler is started, it's not actually "scheduled to run". Now you can check whether the task is present in the scheduler.

Have you included tests for your changes?

👍

Did you document any new/modified functionality?

• Updated example_test.go
• Updated README.md

Notes