Version 0.6.0

This release includes major contributions from @philippjfr (overall maintenance and bugfixes) and @jsignell (reference gallery), plus additional contributions from @slamer59 (environment), @anitagraser (examples), @itcarroll (color_key alias), @Timothy-W-Hilton (bugfix), @jbednar (bugfix), @SandervandenOord (fontscale), and @jordansamuels (doc fixes).

New features:

• Added (a start to) a reference gallery (#302, #357, #359, #360, #361)
• Improved save and show utilities (#451)
• Improved compatibility for tab completion (#411)
• Major performance enhancement with Datashader in some cases (#465)
• Add support for cuDF (#454, #466)
• Support by argument for categorical aggregation (#461)
• Support color_key alias (#446, #458)
• Support spatialpandas for large sets of polygons (#459)
• Add fontscale keyword (#397)
• Added heat and trees example to topics (#378)

Bug fixes and compatibility:

• Fixed 'title_format' deprecation warning (#428)
• Fix networkx documentation (#476)
• Avoid sorting overlays, to make color cycles consistent (#475)
• Replaced sphinx_pyviz_theme with sphinx_holoviz_theme (#366)
• Removed references to pyviz (#373)
• Update environment.yml (#356)
• Misc bugfixes/updates (#387, #403, #408, #439, #447, #448, #449, #450, #452, #453, #456, #467)