use Enum.Parse and ToString methods as fallback for read/write

[leandromoh]

when enum is not a "simple" value in enum...

reading

• before: throw exception
• after: call Enum.Parse of .NET

writing

• before: format/serialize value as interger
• after: call ToString of .NET

this way we guarantee that for weird/corner cases everything still works as expected while maintaining code still optimized for "simple" values of enum (most common use).