Make python API more Pythonic

[kitizz]

For example change

fig.set("axis.data", {'x': x, 'y': y})

To also work with any of the following:

fig.set("axis.data", x, y)
fig.set("axis.data", y)
fig.set("axis.data", x=x, y=y)
fig.set("axis.data", x=x)
fig.set("axis.data", y=y)
fig.set("axis.data", x, y, lineWidth=3)

[kitizz]

Or better yet, allow something like:

fig.axis.data.x = x
fig.axis.data.y = y

data = fig.axis.data
data.set(x=x, y=y)

And related to #40 and #41:

fig.axis.data.x.append([10, 11])
fig.axis.data.y.append([9, 5])
fig.axis.shapes.append(Rectangle(...))