Use plurals for valid/invalid input get in InputFilterInterface

[weierophinney]

InputFilterInterface::getValidInput():array and InputFilterInterface::getInvalidInput():array should be InputFilterInterface::getValidInputs():array and InputFilterInterface::getInvalidInputs():array

Both method return always a collection type (array)

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Originally posted by @Maks3w at zendframework/zend-inputfilter#21

[weierophinney]

I made a pull request for it: zendframework/zend-inputfilter#98

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Originally posted by @jeanCarloMachado at zendframework/zend-inputfilter#21 (comment)