Stripe fix

[CommonClimate]

@khider since you had reported the issue, you have the honor of reviewing the PR. I've redesigned the code so it utilizes MPL's pcolormesh under the hood, which has the added benefit of allowing for multiple colormaps (see docstring for examples).

import pyleoclim as pyleo
nino3 = pyleo.utils.load_dataset('NINO3')
fig, ax = nino3.stripes(show_xaxis=True)

generates:

while for MultipleSeries, this:

import pyleoclim as pyleo
co2ts = pyleo.utils.load_dataset('AACO2')
lr04 = pyleo.utils.load_dataset('LR04')
edc = pyleo.utils.load_dataset('EDC-dD')
ms = lr04.flip() & edc & co2ts # create MS object
fig, ax = ms.stripes(figsize=(8,2.5),show_xaxis=True, sat = 0.8)

generates that:

I have tried to rely on the plotting.py function and make it as general as possible, but it might not be perfect. I need to move on to geoSeries, so this will have to do. It looks like it fixes bug #281 , which is what matters here.