Plotting: Add line markers (#363)

* initial work on markers

* clippy fix

* simplify marker

* use option for color

* prepare for more demo plots

* more improvements for markers

* some small adjustments

* better highlighting

* don't draw transparent lines

* use transparent color instead of option

* don't brighten curves when highlighting

* update changelog

* avoid allocations and use line_segment

* compare against transparent color

* create new Points primitive

* fix doctest

* some cleanup and fix hover

* common interface for lines and points

* clippy fixes

* reduce visibilities

* Update egui/src/widgets/plot/mod.rs

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* Update egui/src/widgets/plot/mod.rs

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* Update egui_demo_lib/src/apps/demo/plot_demo.rs

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* Update egui_demo_lib/src/apps/demo/plot_demo.rs

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* changes based on review

* fix test

* dynamic plot size

* remove height

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

CHANGELOG.md

@@ -8,6 +8,7 @@ NOTE: [`eframe`](eframe/CHANGELOG.md), [`egui_web`](egui_web/CHANGELOG.md) and [
 ## Unreleased
 
 ### Added ⭐
+* [Line markers for plots](https://github.com/emilk/egui/pull/363).
 * Add right and bottom panels (`SidePanel::right` and `Panel::bottom`).
 * Add resizable panels.
 * Add an option to overwrite frame of a `Panel`.
@@ -18,6 +19,7 @@ NOTE: [`eframe`](eframe/CHANGELOG.md), [`egui_web`](egui_web/CHANGELOG.md) and [
 * `TextEdit` now supports edits on a generic buffer using `TextBuffer`.
 
 ### Changed 🔧
+* Plot: Changed `Curve` to `Line`.
 * `TopPanel::top` is now `TopBottomPanel::top`.
 * `SidePanel::left` no longet takes the default width by argument, but by a builder call.