Improve the name generation for code extraction

[sonmarcho]

This PR drastically improves the generated names in particular by making them simpler.

It also solves #87 by making a distinction between the name elements used for "regular" impl blocks and those used for trait impl blocks. This allows us to use the trait references as a name for those impl blocks.

For instance, consider the following Rust code:

impl<T> BoolTrait for Option<T> {
    fn get_bool(&self) -> bool {
        ... // Omitted
    }
}

While before we generated:

/- [traits::{core::option::Option<T>#1}::get_bool] -/
def Option.get_bool (T : Type) (self : Option T) : Result Bool := ... -- Omitted

def BoolTraitOption (T : Type) : BoolTrait (Option T) := {
  get_bool := BoolTraitOption.get_bool T
}

We now generate:

/- [traits::{(traits::BoolTrait for core::option::Option<T>)#1}::get_bool] -/
def BoolTraitOption.get_bool (T : Type) (self : Option T) : Result Bool := ... -- Omitted

def BoolTraitOption (T : Type) : BoolTrait (Option T) := {
  get_bool := BoolTraitOption.get_bool T
}