- implement [classpath] which adds a path to the global path, like what
  [declare -stdpath] does.  The idea is that the global path serves as a
  Java-style classpath. and the local path serves as the namespace.

  - inlet accepts bang to output classpath on outlet
  - inlet accepts messages to add items to the classpath
  - follows same interface as [textfile], [qlist]

- implement [import] which adds the libdir path to the canvas path, similar
  [declare -lib] does, except that it only looks in the global path (aka
  classpath)

  - inlet accepts bang to output canvas path on outlet
  - inlet accepts messages to add items to the canvas path
  - follows same interface as [textfile], [qlist]

- make [libdir] load libdirs when they are called with [import] and [declare
  -lib] and [declare -stdlib].

- [libdir] loader should only add the libdir to the helppath, not the
  additional doc/5.reference path to the helppath.  The idea is that libdirs
  are self-contained.


- test binary on 0.41 test