The klish-2.0.0 contains many changes. The main ones is plugin subsystem and user defined hooks.
The user can create his own shared library (.so file) with special API and export symbols to use as builtin functions within ACTION. Also shared object can export its own hooks (hook for access, for communication to confd, ...).
The plugin using is controlled by XML files. There are new tags: PLUGIN and HOOK. So to use your own C-based code with klish you don't need to recompile klish. Just create a plugin. See plugin examples in plugin/ dir within klish source tree.