#5 Add description for verifiers

...dmn/verification/verifier/impl/IdenticalRuleVerifier.java

...ore/dmn/verification/verifier/types/DateVerification.java

.../verification/verifier/types/EmptyOutputVerification.java

...fication/verifier/types/EquivalentStringVerification.java

...erification/verifier/types/IdenticalRuleVerification.java

...fication/verifier/types/InputValueSyntaxVerification.java

...ification/verifier/types/LonelyDataInputVerification.java

...cation/verifier/types/MissingInputColumnVerification.java

...fication/verifier/types/MissingInputDataVerification.java

.../verification/verifier/types/MissingRuleVerification.java

.../verification/verifier/types/OverlappingVerification.java

...fication/verifier/types/PartialReductionVerification.java

...n/verifier/types/PredefinedExistingValueVerification.java

...on/verifier/types/PredefinedMissingValueVerification.java

.../verification/verifier/types/SubsumptionVerification.java

dmnverifierapi/verifier.md