Add Base Class for Handling EnkaNetwork Errors

[luoshuijs]

Our hope is to create a base class that can gracefully catch exceptions thrown from the EnkaNetwork.py module

class EnkaNetworError(Exception):
    """Base class for EnkaNetwork errors."""


class NetworkError(EnkaNetworError):
    """Base class for exceptions due to networking errors."""


class TimedOut(NetworkError):
    """Raised when a request took too long to finish."""


class BadRequest(EnkaNetworError):
    """Raised when EnkaNetwork could not process the request correctly."""


class EnkaValidateFailed(BadRequest):
    """Exception that's raised for when status code 400 occurs."""


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