Add recover operator to Eval

[johnmcclean]

Support general and specific error handling within a lazy or reactive Eval chain

Eval<T> recover(Function<Throwable,? extends T> value);
Eval<T> recover(Class<C> type, Function<? super C,? extends T> value)

E.g. with general error handling

Eval.now(100)
    .map(i->{throw new RuntimeException();})
    .recover(i->120)
    .get() //120

E.g. with specific error handling

Eval.now(100)
    .map(i->{throw ExceptionSoftener.softenException(IOException())})
    .recover(IOException.class,i->120)
    .get() //120

[johnmcclean]

Part of #986

[johnmcclean]

Released in 10.1.1