To create a new experiment-specific configuration variable, define
extra_parameters in your
def extra_parameters(): config.register('n', int, , False)
'n' is a string with the name of the parameter,
int is its type,
 is a list of synonyms that be used to access the same parameter, and
False is a boolean signifying that this configuration parameter is not
sensitive and can be saved in plain text. Once defined in this way, a
parameter can be used anywhere that built-in parameters are used.
validators parameter can also be passed, which must be either
None or a list of callables that take a single argument (the value of the config)
and may raise a
ValueError describing why the value is invalid.