Aliasing a Feature

[MatthieuDartiailh]

The recent discussions in LabPy/lantz_drivers#3 and the corresponding implementation attempt suggest to add aliasing capabilities to features.

• in some cases the standard requires a setting per channel but actually the setting is global, aliasing the channel feature to a common driver feature would allow to avoid sync issue (and could be tracked by the hooks needed by the qt backend/the proxies). To handle this I propose to add an Alias Feature taking the name of the aliased feature (using dot for parent access) and an aliases attributes to the base Feature class to easily keep track of aliases.
• in other cases we duplicate a Feature because we need a low/high combination but the driver treat them in a symmetric manner (low = -high). Following the same idea of Aliases we could have a LinkedTo Feature specifying a master Feature and getting/setting relations.