implement parameter update for add_values()

[bablokb]

This commits adds an optional parameter update=True to add_values(). The default keeps the current behavior. Setting update=False results in primitives not being updated, this has to be done manually after adding a number of values.

Timing tests with a slightly modified version of examples/display_shapes_sparkline_simpletest.py:

s = time.monotonic()
for _ in range(10):
    sparkline1.add_value(random.uniform(0, 10))
print("%f" % (time.monotonic()-s))

vs:

s = time.monotonic()
for _ in range(10):
    sparkline1.add_value(random.uniform(0, 10),update=False)
sparkline1.update()
print("%f" % (time.monotonic()-s))

The first version maxes out at about 2 seconds after the limit of 40 values is reached, the second version maxes out at 0.2 seconds. Figures measured with a PyPortal.

[kmatch98]

Makes sense to me, gives more redraw flexibility when adding multiple points.