block decorator parameterization and simpler signal names when needed

[jvillar]

Since the introduction of the block decorator, all functions in the calltrace of a design, have to be decorated by it. This way, all these functions make a contribution to the name of its internal signals. This behaviour prevents name duplication and is the desired behaviour in most cases.

But there are times that intermediate functions don’t generate hardware generators nor any kind of myhdl objects, signals, etc… However they introduce a very high complexity in the converted code, that renders it unreadable. After some discussion at MyHDL discourse forum (https://discourse.myhdl.org/t/simplified-signal-naming-when-possible/403), I modified the MyHDL block decorator to accept conversion arguments so the conversion process can be parameterized. In this PR a new feature is introduced to make it possible to explicitely mute some hierarchy levels regarding to signal naming.

I think this can be a good starting point for parameterizing the conversion process.