a zero length command (now, no chain) used to stop the streaming.
Now it seems to do the reverse... must investigate.
Made all clock configuration into enums. The strings were painful
and there cant be that many variations that enums cant cover them.
The enums will make more sense to developers than mystery strings.
Created structs to replace range tuples, and clock config struct.
Merged clock config props into one property using config struct.
Added templated dict construction to use the assign::map_list_of.
Added gcc flag to set visibility to hidden and use the api macro.
