Subclass SchemaError for default errors such as 'Wrong keys', 'Missing keys' 'Wrong Type'

[bernalrs]

I would like to suggest a simple change that would see the introduction of some new Error/Exception derived from SchemaError which would serve the purpose.

As of verson 0.6.1:

1. raise SchemaError('Wrong keys %s in %r' % (s_wrong_keys, data), e.format(data) if e else None)
2. raise SchemaError('Missing keys: ' + s_missing_keys, e)
3. SchemaError('%r should be instance of %r' % (data, s.__name__), e.format(data) if e else None)

into

1. class SchemaWrongKeyError(SchemaError):
2. class SchemaMissingkeysError(SchemaError):
3. class SchemaUnexpectedTypeError(SchemaError)

Thanks

[skorokithakis]

As long as these exceptions inherit from SchemaError, this looks good to me. Is there any possibility that something could be adversely impacted?

[bernalrs]

As long as we do not change the error message we should be OK. This should allow developers to catch specific exception and re-throw them when using this library in the application code.

[bernalrs]

Might be worth adding these new type in the README.md do you agree ?

[skorokithakis]

Yes :( I forgot about that and already released 0.6.2... Would you like to do the honours of documenting the errors?