the current value for a configuration option. Some configuration
options (like the ExitPolicy) can have multiple values. This provides a
**list** with all of the values if **multiple** is **True**. Otherwise this
will be a **str** with the first value.

If provided with a **default** then that is provided if the configuration
option was unset or the query fails (invalid configuration option, error
response, control port closed, initiated, etc).

If the configuration value is unset and no **default** was given then this
provides **None** if **multiple** was **False** and an empty list if it was
**True**.

:param str param: configuration option to be queried
:param object default: response if the option is unset or the query fails
:param bool multiple: if **True** then provides a list with all of the
  present values (this is an empty list if the config option is unset)

:returns:
  Response depends upon how we were called as follows...

  * **str** with the configuration value if **multiple** was **False**,
    **None** if it was unset
  * **list** with the response strings if multiple was **True**
  * default if one was provided and the configuration option was either
    unset or our call failed

:raises:
  * :class:`stem.ControllerError` if the call fails and we weren't
    provided a default response
  * :class:`stem.InvalidArguments` if the configuration option
    requested was invalid
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