message name changes
ISBN10 and ISBN13 validators added
small fix: use self.messages instead of ISBNTestsMixin.messages
create reusable mixin of testcase for Numeric validators
add Float validator
add Decimal validator (resolves #9)
add AnyOf validator (implementation + UTs)
add BaseEnum, Enum and MultiEnum validators (resolves #18)
add Boolean validator (resolves #17)
DateTime validator implementation (resolves #10)
implementation of EqualTo validator (resolves #15)
implementation of Password validator (resolves #16)
split module with base validators into two modules

Leave real base classes in base.py and create general.py for other classes (and
similar with test modules).