Inconsistent capitalisation of plot recipes names

[owiecc]

Recipe names have inconsistent capitalisations. By convention Pascal case is used:

• ABLines
• BarPlot
• DataShader
• HLines
• ScatterLines
• StreamPlot

However, there are a few recipes that stray from this convention:

• Voronoiplot
• Tricontourf
• Errorbars

[owiecc]

This is pretty important for https://github.com/MakieOrg/AlgebraOfGraphics.jl where recipes are used instead of plotting functions.

[jkrumbiegel]

I guess we could change their names and add and export const Voronoiplot = VoronoiPlot for backwards compat

[asinghvi17]

This should also be made clear in the recipes page and the docstring for the recipe and block macros!

[ffreyer]

I think we need to figure out some stricter naming rules in general. I.e. fix #2555 too, and probably revive #2520

[jkrumbiegel]

I think our attribute naming problems just mirror general Julia naming problems, because the convention to not use underscores is broken whenever it looks bad to the committer. But maybe it's not so important anymore after 0.21 when unknown attributes will error, as you're then reminded more easily of the correct form.