migration notes and exceptions about MPL compat.

MPL compat does not work with MPL 2.0, and is unlikely to ever until or unless MEP 25 is implemented. The 0.12.5 release notes should make mention of this, and importing the MPL compat fiunctions should raise an error if MPL >= 2.0 is installed.

[bryevdv]

I’m not categorically opposed to making Holoviews the “high level API for Bokeh” but to do that needs some things:

• a decision to that effect
• commitment of resources
• a plan to market/advertise/demonstrate the results widely in the bokeh docs

[pzwang]

One additional comment: I’d like to make sure that blocking on MEP-25 is not a “perfect is the enemy of the good” situation. Not being able to offer seaborn compatibility is really not great, especially given the situation with bokeh.charts. (Altair not a viable alternative because it is still very new and not widely adopted or documented, although I expect it will get there in the fullness of time.)

Without a good high-level charting API, we are left with a structural, strategic deficiency.