added getValues() method to validator to conveniently retrieve all values at once
modified toBoolean(): undefined and null are converted to false
added hasValue() method to conveniently check if a value
is set at all (fails with undefined, null and the empty string)
modified length validations to fail without exception
if the value is not a string
Merge pull request #5 from grob/validations

adds getValues() and hasValue()