Created by: cgensoul
Added optional params support in API operations
This PR translates optional OpenAPI operation parameters into optional OCaml function parameters. To allow more flexible use of generated API functions, all function parameters are now named (even the required ones).
Default values given for API operation parameters are also turned into default values for corresponding parameters of OCaml generated API function. Default values are also automatically generated for parameters that are of an enum type with a uniq enum case (useless parameter since it's value is constant but encountered...).
A bug has been fixed in path param replacement. Reformatted api-impl template to make it easier to read.