Revert Maybe Change from 0.12.1

[Tankanow]

Revert Breaking Maybe change in 0.12.1

It seems like the Maybe change to propagate error information (#411) was not intended to be a breaking change. Unfortunately, this is a breaking change because many consumers rely on Any's short-circuiting behavior. That is, the following code now does not do the same thing anymore:

def validator_that_raises_typeerror(x):
    if x is None:
        raise TypeError('Ooops')
    return x

s = Maybe(validator_that_raises_typeerror)

# pre 0.12.1
s(None)  # => returns None

# post 0.12.1
s(None)  # => throws TypeError

You can argue that the validator above is malformed, and you may be right; however, it doesn't change the fact that voluptuous currently allows that validator and the Maybe change results in different behavior, not just more error information.