Typescript fetch update

[leonyu]

• Add npmName and npmVersion
  • will take a look at npmRepository and snapshot since my use case doesn't take advantage of those
• Make sure compilable in both ES6 and ES5
• Fix enum implementation (was broken in the PetStore)
  • this implementation uses string literals for string enums instead of Enum (maybe this would be better served as an option) since TypeScript Enum follows C Enum instead of Java Enum that defaults to a number. see ref

[wing328]

@leonyu thanks for the contribution. PR merged into master.