plt.subplots crashes when handed fig_kw argument

[dstansby]

Current docs (http://matplotlib.org/devdocs/api/pyplot_api.html#matplotlib.pyplot.subplots) list fig_kw as one of the arguments that can be passed to plt.subplots, however this fails with:

import matplotlib.pyplot as plt
fig, axs = plt.subplots(1, 2, fig_kw={'figsize': (15, 8)})

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/dstansby/matplotlib/lib/matplotlib/pyplot.py", line 1190, in subplots
    fig = figure(**fig_kw)
  File "/home/dstansby/matplotlib/lib/matplotlib/pyplot.py", line 544, in figure
    **kwargs)
  File "/home/dstansby/matplotlib/lib/matplotlib/backends/backend_qt5agg.py", line 43, in new_figure_manager
    thisFig = FigureClass(*args, **kwargs)
TypeError: __init__() got an unexpected keyword argument 'fig_kw'

Either the docs should be updated to note that anything extra handed to plt.subplots is handed to plt.figure, or fig_kw should be an allowed argument.

[dopplershift]

fig_kw isn't documented as a keyword argument itself--what it's saying is that all additional kwargs are passed onto the Figure constructor.

[dopplershift]

Oh, now I see that it's listed as an optional dict in the parameters section--that part should be changed to reflect what I said above.