add job uuids and change scheduler job slice to map

[JohnRoesler]

What does this do?

• adds a uuid to each job
• changes the scheduler jobs slice to be a map
  • this increases job removal performance, can be by ID now
  • also makes several other looks up more efficient doing map key lookup instead of looping slice

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

resolves #526

List any changes that modify/break current functionality

• removes the Swap and Less methods on the scheduler that were implemented for sorting jobs

Have you included tests for your changes?

Did you document any new/modified functionality?

• Updated example_test.go
• Updated README.md

Notes