Review documentation of Axes plotting methods #10148

As a follow up of #7205, some docstrings of the basic Axes plotting methods could need a bit care. In particular:

• Conversion to numpydoc format.
• Improvements on the descriptions.

I intend to go through the methods and update their docs. This is a summary issue to keep track of my progress:

Basic

• Axes.plot
• Axes.errorbar
• Axes.scatter
• Axes.plot_date
• Axes.step
• Axes.loglog
• Axes.semilogx
• Axes.semilogy
• Axes.fill_between
• Axes.fill_betweenx
• Axes.bar
• Axes.barh
• Axes.stem
• Axes.eventplot
• Axes.pie
• Axes.stackplot
• Axes.broken_barh
• Axes.vlines
• Axes.hlines
• Axes.fill

Spans

• Axes.axhline
• Axes.axhspan
• Axes.axvline
• Axes.axvspan

Spectral

• Axes.acorr
• Axes.angle_spectrum
• Axes.cohere
• Axes.csd
• Axes.magnitude_spectrum
• Axes.phase_spectrum
• Axes.psd
• Axes.specgram
• Axes.xcorr

Statistics

• Axes.boxplot
• Axes.violinplot
• Axes.violin
• Axes.bxp

Binned

• Axes.hexbin
• Axes.hist
• Axes.hist2d

Contours

• Axes.clabel
• Axes.contour
• Axes.contourf

Array

• Axes.imshow
• Axes.matshow
• Axes.pcolor
• Axes.pcolorfast
• Axes.pcolormesh
• Axes.spy

Unstructured triangles

• Axes.tripcolor
• Axes.triplot
• Axes.tricontour
• Axes.tricontourf

Text and Annotations

• Axes.annotate
• Axes.text
• Axes.table
• Axes.arrow

Fields

• Axes.barbs
• Axes.quiver
• Axes.quiverkey
• Axes.streamplot

Axes limits and direction

• Axes.invert_xaxis
• Axes.xaxis_inverted
• Axes.invert_yaxis
• Axes.yaxis_inverted
• Axes.set_xlim
• Axes.get_xlim
• Axes.set_ylim
• Axes.get_ylim
• Axes.update_datalim
• Axes.update_datalim_bounds
• Axes.set_xbound
• Axes.get_xbound
• Axes.set_ybound
• Axes.get_ybound

Axes scales

• Axes.get_xscale
• Axes.set_xscale
• Axes.get_yscale
• Axes.set_yscale

Note: I currently update the docstrings in my private branch https://github.com/timhoffm/matplotlib/tree/axes-plotting-docstrings and will provide a pull request once I'm done. I think this is better than opening a separate pull request for every change. Please let me know, in case you'd rather prefer many smaller PRs.

The fixes will be supplied in a series of PRs referencing this issue.