Allow for generics with either or types

[dereckmezquita]

Description

Much in the same way that TypeScript allows for Union Types, we can allow for Union Types in the interface package.

Implementation Ideas

CharNumList <- interface("list",
    value = c("character", "numeric")
)

# Implement the interface
list1 <- implement(CharNumList, list("John", 30))

Df <- interface("data.frame",
    name = "character",
    height = c("numeric", "character"),
    age = "numeric"
)