Better docs for updated 2.5.6 isUnique

Added text to the isUnique docs to describe how the validation behaves when a specified field isn't included in the model data
Merge pull request #1981 from watermark/patch-1

Better docs for updated 2.5.6 isUnique
Typo in documentation

Missed one letter ;)
Merge pull request #1982 from trajakovic/patch-1

Typo in documentation for Hash utility