Eval enhancements : Monix inspired RX style operators

[johnmcclean]

Monix's Coeval offers a number of very useful enhancements to Eval.
They are

• doOnFinish : triggered when Eval execution completes
• restartUntil : retry the Eval until a predicate holds
• onErrorXXX : switch eval instances and otherwise handle errors

It would be useful to add error handling and completition events to Cyclops Eval.

• onComplete : pass the completed value into the provided Consumer
• onErrorSwitch : switch Eval is an exception occurs
• onErrorRestart : restart the Evaluation if an error occurs up to a set number of retries

Potentially unsafe Operators to think about.

• restartUntil : retry the Eval until a predicate holds, may make it too easy to create runtime infinite loops

[johnmcclean]

Naming

• onErrorSwitch is recoverWith
• doOnFinish should be onComplete

[johnmcclean]

Released in 10.3.0