use string value when encoding enums

[etan-status]

Currently, we encode enum values always as the numeric value ord(val). unless explicitly overridden using serializesAsTextInToml or with a custom writeValue implementation. Reduce verbosity by automatically doing that.

[etan-status]

Defaults:

• Parse from string, do not parse from int (for numeric enums, can be turned on via template when necessary)
• Encode to string

By default, string comparison is strict, as in, it must match string exactly. A template is available to relax that constraint.