Export of undefined symbols

[gennadiryan]

Several instances of symbols exported by a module but not defined in the given module have been found. In particular, src/dynamics.jl exports dynamics_hessian_of_lagrangian, which is undefined in module Dynamics.

This is possible because of the permissibility of "late binding" in Julia; for instance, the declaration of a module-global variable at runtime.

Has implications for usability of pypiccolo in a REPL.

NOTE: If there is justification for keeping the symbol around, despite lacking an implementation, defining a stub as in function dynamics_hessian_of_lagrangian end is sufficient to prevent implications on pypiccolo REPL usability.