Highlights of this release include:
- Figure and Axes creation / management
- New subfigure functionality
- Single-line string notation for `subplot_mosaic`
- Changes to behavior of Axes creation methods (`gca`, `add_axes`, `add_subplot`)
- `add_subplot`/`add_axes` gained an *axes_class* parameter
- Subplot and subplot2grid can now work with constrained layout
- Plotting methods
- `axline` supports transform parameter
- New automatic labeling for bar charts
- A list of hatches can be specified to `bar` and `barh`
- Setting `BarContainer` orientation
- Contour plots now default to using `ScalarFormatter`
- `Axes.errorbar` cycles non-color properties correctly
- `errorbar` *errorevery* parameter matches *markevery*
- `hexbin` supports data reference for *C* parameter
- Support callable for formatting of Sankey labels
- `Axes.spines` access shortcuts
- New `stairs` method and `StepPatch` artist
- Added *orientation* parameter for stem plots
- Angles on Bracket arrow styles
- `TickedStroke` patheffect
- Colors and colormaps
- Collection color specification and mapping
- Transparency (alpha) can be set as an array in collections
- pcolormesh has improved transparency handling by enabling snapping
- IPython representations for Colormap objects
- `Colormap.set_extremes` and `Colormap.with_extremes`
- Get under/over/bad colors of Colormap objects
- New `cm.unregister_cmap` function
- New `CenteredNorm` for symmetrical data around a center
- New `FuncNorm` for arbitrary normalizations
- GridSpec-based colorbars can now be positioned above or to the left of the main axes
- Titles, ticks, and labels
- supxlabel and supylabel
- Shared-axes `subplots` tick label visibility is now correct for top or left labels
- An iterable object with labels can be passed to `Axes.plot`
- Fonts and Text
- Text transform can rotate text direction
- `matplotlib.mathtext` now supports *overset* and *underset* LaTeX symbols
- *math_fontfamily* parameter to change `Text` font family
- `TextArea`/`AnchoredText` support *horizontalalignment*
- PDF supports URLs on Text artists
- rcParams improvements
- New rcParams for dates: set converter and whether to use interval_multiples
- Date formatters now respect *usetex* rcParam
- Setting *image.cmap* to a Colormap
- Tick and tick label colors can be set independently using rcParams
- 3D Axes improvements
- Errorbar method in 3D Axes
- Stem plots in 3D Axes
- 3D Collection properties are now modifiable
- Panning in 3D Axes
- Interactive tool improvements
- New `RangeSlider` widget
- Sliders can now snap to arbitrary values
- Pausing and Resuming Animations
- Sphinx extensions
- `plot_directive` *caption* option
- Backend-specific improvements
- Consecutive rasterized draws now merged
- Support raw/rgba frame format in `FFMpegFileWriter`
- nbAgg/WebAgg support middle-click and double-click
- nbAgg support binary communication
- Indexed color for PNG images in PDF files when possible
- Improved font subsettings in PDF/PS
- Kerning added to strings in PDFs
- Fully-fractional HiDPI in QtAgg
- wxAgg supports fullscreen toggle