Add examples to Javadoc for Throwing*.of factory methods

[sbrannen]

The current Javadoc is technically correct, but it is not readily apparent how the methods are intended to be used.

In order to help developers understand how the Throwing*.of factory methods can be used, we should add an example or two to the Javadoc of each of the following methods.

• ThrowingConsumer.of(ThrowingConsumer<T>)
• ThrowingFunction.of(ThrowingFunction<T>)
• ThrowingBiFunction.of(ThrowingBiFunction<T, U, R>)
• ThrowingSupplier.of(ThrowingSupplier<T>)