Register a library. A list of registered libraries can be fetched by
calling LibUtils.getRegisteredLibraries(). If you write a library
of scripting functions, plug-ins that rely on that library can check if it
is available through the registry service, and registered librarys will
be included in the built-in library help system.
Returns true if library is a registered library.
If the library has not been previously registered, but the library exists,
then it will be registered immediately and this function
will return true. Otherwise, this method returns false.