ECS chapter structure (#288)

I intend to close and split #182 to improve both development and review workflows.

This is a tiny PR to make reviewing that work less painful by reducing weird branch issues.

content/learn/book/ecs/commands/_index.md

@@ -1,13 +1,7 @@
 +++
-title = "Manipulating entities with commands"
-weight = 4
+title = "Commands queue up work"
+weight = 5
 template = "book-section.html"
 page_template = "book-section.html"
 insert_anchor_links = "right"
 +++
-
-TODO: explain what commands are used for
-
-TODO: explain that they only run at the end of the stage, mention that they have exclusive world access
-
-TODO: show how to spawn, despawn and modify entities with commands

content/learn/book/ecs/detecting-changes/_index.md

@@ -0,0 +1,7 @@
++++
+title = "Detecting changes"
+weight = 6
+template = "book-section.html"
+page_template = "book-section.html"
+insert_anchor_links = "right"
++++

content/learn/book/ecs/ecs-magic/_index.md

@@ -0,0 +1,7 @@
++++
+title = "Understanding the magic"
+weight = 8
+template = "book-section.html"
+page_template = "book-section.html"
+insert_anchor_links = "right"
++++

content/learn/book/ecs/exclusive-world-access/_index.md

@@ -1,6 +1,6 @@
 +++
-title = "Exclusive `World` access"
-weight = 8
+title = "Exclusive world access"
+weight = 7
 template = "book-section.html"
 page_template = "book-section.html"
 insert_anchor_links = "right"

content/learn/book/ecs/queries/_index.md

@@ -0,0 +1,7 @@
++++
+title = "Fetching data with queries"
+weight = 2
+template = "book-section.html"
+page_template = "book-section.html"
+insert_anchor_links = "right"
++++

content/learn/book/ecs/systems/_index.md

@@ -0,0 +1,8 @@
++++
+title = "Systems do work"
+weight = 4
+template = "book-section.html"
+page_template = "book-section.html"
+insert_anchor_links = "right"
++++
+