`chain_prop` docstring entry missing in `matplotlib` `plot_trace()`

Describe the bug chain_prop argument entry in matplotlib backend of plot_trace() docstring is missing.

It exists downstream at https://github.com/arviz-devs/arviz/blob/57aeded2fff88a646939fc36e5b2a86a0cf718b0/arviz/plots/traceplot.py and could be reproduced. But I’d like more information about valid properties that can be cycled. Can linestyle, color, lw, alpha, etc be used?

Also, somewhat related, I think that with the black formatting, this chunk at https://github.com/arviz-devs/arviz/blob/57aeded2fff88a646939fc36e5b2a86a0cf718b0/arviz/plots/backends/matplotlib/traceplot.py#L148-L155

would be clearer to read as:

        if chain_prop is None:
            chain_prop = {"linestyle": ("solid", "dotted", "dashed", "dashdot")}

[hectormz]

And the docstring examples need to be updated since compact=True is the default now.

Examples 2 and 5 (https://arviz-devs.github.io/arviz/api/generated/arviz.plot_trace.html) should be updated.

Example 2 should be (to illustrate what changing compact achieves):

az.plot_trace(data, compact=False)

and Example 5 should be

lines = [("theta_t", {'school': "Choate"}, [-1])]
az.plot_trace(data, var_names=('theta_t', 'theta'), coords=coords, lines=lines, compact=False)

or

lines = [("theta_t", {}, [-1])]
az.plot_trace(data, var_names=('theta_t', 'theta'), coords=coords, lines=lines)

and maybe consider whether the function should actually be changed to accommodate an ‘over-specified’ lines

lines = (('theta_t',{'school': "Choate"}, [-1]),)

az.plot_trace(data, var_names=('theta_t', 'theta'), coords=coords, lines=lines)

[hectormz]

Right, basically anything on this matplotlib page is valid:

chain_prop={"linestyle": ("-","--"), "color":("red","green", "blue", "purple"), "linewidth":(1,4)},
chain_prop="color",
chain_prop={"dashes":((2,4),(1,5))}
chain_prop={"marker":["o","^"]}
chain_prop=None # defaults to pre-defined `linestyle` if `compact` is True

I realize that the high-level docstring should be updated to describe it as a dict instead of tuple:

    chain_prop: str or dict {str: array_like}, optional
        Tuple containing the property name and the property values to distinguish diferent chains

and maybe compact_prop needs to be updated, too