Updates to FSM and Pipeline abstractions and documentation

[mkorbel1]

Description & Motivation

• Renamed StateMachine to FiniteStateMachine (deprecated StateMachine name)
• Expose mapping from StateIdentifier to state index in FiniteStateMachine
• Deprecated clk on Pipeline and FiniteStateMachine abstractions
• Allow FiniteStateMachine states to use "priority" (and "none") instead of only "unique".
• Add support for multi-trigger support for the Sequentials in FiniteStateMachine and Pipeline abstractions
• Refactor the "traffic light FSM" to use newer features from Dart and FiniteStateMachine to be more readable as a helpful example
• Update the FSM documentation in the user guide to be more helpful

Related Issue(s)

Fix #409
Fix #372
Fix #406
Fix #400

Testing

Modified some tests to cover functionality added

Backwards-compatibility

Is this a breaking change that will not be backwards-compatible? If yes, how so?

Some deprecations, but no backwards compatibility breaking changes

Documentation

Does the change require any updates to documentation? If so, where? Are they included?

Updated some docs and API docs