merge multiplexers for fixed steps and variable steps
There are two different multiplexers for step handlers, one dedicated to variable steps, and one dedicated to fixed steps. The later also can only manage handlers that use the same size. Everything should be merged into a more feature-rich multiplexer, allowing fixed and variable size steps, several sizes for variable sizes, and also removal of handler. This is would also be used internally for implementing issue #809 (closed)
Edited by Luc Maisonobe