Added function, mu-codefile.el
mu-base.el: Moved `mu-base-maptree` family to the start.
mu-base.el: Added utility functions `mu-base-string-abbreviate`, `mu-base-npushlast`, `mu-base-string-join`, `mu-filter`, mu-with-file`.
mu-codefile.el: added.
resources/test.codefile.example.el: added.