[Rust] Enhance enum supporting fromstr and display and into

[wbprime]

This pr intended to make generated enum items impl FromStr and Display and Into trait.

Usually an enum (in or not in trading) may have two different usecases: either for integer-compitible values (like Side/OrderType) or for string values (like Market). It's very kind to generate conversion helper for generated Rust enum types. Currently only From was impl for enum types.

1. FromStr trait

   Consider a Market enum:

   enum Market {
   XSHE, XSHG, 
   }

   A str to Market conversion was usually needed when dealing with external system.

2. Display trait

   See above Market enum, a Display trait impl was helpful when converting to meaningful string representation for display or presentation purpose.

3. Into trait

   As a reverse op of From, it is also helpful to get sensible storing data into DB or something similar.