Improving current standard library

[thomasvergne]

While having a new extension system, the standard library should now take advantage of it by providing generic interfaces and defining repetitive behaviors within types. Such basic interfaces should be added:

• traversable: for everything related to list and list-like data-structures
• show: to convert a type to a str value
• numeric: to provide basic algebra on every type (such as string concatenation enabled by the + operator)
• ordering: to enable ordering on other types than numbers
• boolean: to provide boolean algebra (and, or, and not functions)
• default: to define a default value for a type (Haskell equivalent to mempty with Monoid type-class)
• and other interfaces..

These interfaces would come with their respective basic extensions. For instance, there should be an instance of show for every core data type, as there should also be type extensions of the other core interfaces.