New rcParams for dates: set converter and whether to use interval_multiples
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The new :rc:`date.converter` allows toggling between
`matplotlib.dates.DateConverter` and `matplotlib.dates.ConciseDateConverter`
using the strings 'auto' and 'concise' respectively.

The new :rc:`date.interval_multiples` allows toggling between the dates
locator trying to pick ticks at set intervals (i.e. day 1 and 15 of the
month), versus evenly spaced ticks that start where ever the
timeseries starts:

.. plot::
    :include-source: True

    import matplotlib.pyplot as plt
    import numpy as np

    dates = np.arange('2001-01-10', '2001-05-23', dtype='datetime64[D]')
    y = np.sin(dates.astype(float) / 10)
    fig, axs = plt.subplots(nrows=2, constrained_layout=True)

    plt.rcParams['date.converter'] = 'concise'
    plt.rcParams['date.interval_multiples'] = True
    ax = axs[0]
    ax.plot(dates, y)

    plt.rcParams['date.converter'] = 'auto'
    plt.rcParams['date.interval_multiples'] = False
    ax = axs[1]
    ax.plot(dates, y)