Fix the implementation of the abridged version of `leftmost', the one
which use `letcc', in order to not ask question about the result of
natural recursion.
Implement a new version of `rember_one_star' which use an interesting
trick with `letcc'.
Refactor unit tests in order to stress the new `rember_one_star'
implementation with `letcc'.
Introduced `try' control flow and used it in `rember_one_star',
very very cool.
Refactor some names after introducing `try' and the result is
*TERRIFIC*, it seems really a declarative programming and that
code will compute by itself!