Add reset concepts

[snowleopard]

There is a subtle difference between initialise and reset concepts:

• initialise indicates the initial state of the circuit.
• reset is used to specify which gates should be equipped with the reset pin that forces gates to the appropriate initial state during the circuit start-up (usually, by connecting them to the rst and nrst wires). This is particularly important for gates with internal memory (e.g. C-elements).

@danilovesky knows much more than I about this, as he implemented a special Reset plugin in Workcraft.

An example:

circuit a b c = cElement a b c <> inputs [a, b] <> outputs [c]
    <> initialise0 [a, c] <> initialise1 [b] -- note that a = 0 and b = 1 do not force c = 0!
    <> reset [c] -- therefore we must reset the C-element at start-up to the desired output value