Changed enum parsing mechanism to be name based

[eladrich]

Changed enum parsing to be based on enum field names instead of values.

As discussed in #8, this allows one to support enums with non-string values such as

class LRMethod1(Enum):
    onecycle: torch.optim.lr_scheduler = OneCycleLR
    lambdalr: torch.optim.lr_scheduler = LambdaLR

Instead of allowing only enums of the form:

class LRMethod2(Enum):
    onecycle: str = "onecycle"
    constant: str = "constant"