Add support for the Comparator interface

[boretti]

The idea is to add something (not yet fully defined) to also support exception in Comparator.

The issue #72 add the required new methods for this issue.

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[boretti]

Here are the different use cases to be supported :

• Error in key extraction
• Error in key comparaison
• Error in compare method itself

This library already supports these three use cases, but documentation or helper methods are required to simplify usage.

Error in key extraction

Key extraction is done by using Function, or ToXXXFunction. It is possible to use the version WithException to protect the execution and define a default return value in case of exception.

Error in key comparaison

Key comparaison is either purely based on primitive type (which should not throw exception) or use a Comparator. In this case, the solution is to protect the compare method.

Error in compare method itself

The Comparator interface is very similar to the ToIntBiFunction once. The main issue here is ensure coherent result. Currently, this library only provides a way (for interface returning primitive) to return default result in case of exception, which may not be suffisant to ensure a coherent result for comparator.