Support numeric value enums

[mreiche]

Is your feature request related to a problem? Please describe.
Enum values beginning with a number will result in VALUE_N keys.

"enum": [
    "1st",
    "2nd"
],

generated enum:

class MyEnum(Enum):
    VALUE_0="1st"
    VALUE_1="2nd"

Describe the solution you'd like
It would be better write the keys as

class MyEnum(Enum):
    VALUE_1ST="1st"
    VALUE_2ND="2nd"

Additional context
Having enums with anonymous VALUE keys are not human-readable.

[NixBiks]

I'd also love to this. In general it would be awesome with literals instead of enums since enums doesn't support all characters - e.g. - is replaced with _.