Port tree traversal material into new analysis tut

And create a stub for tree sequence analysis

Author: hyanwong

_toc.yml

@@ -12,6 +12,10 @@ parts:
   - file: simplification
   - file: metadata
   - file: tskitr
+- caption: Analysis
+  chapters:
+  - file: analysing_tree_sequences
+  - file: analysing_trees
 - caption: Backward time simulations
   # TODO this will be broken down more finely as we add more content
   chapters:

analysing_tree_sequences.md

@@ -0,0 +1,25 @@
+---
+jupytext:
+  text_representation:
+    extension: .md
+    format_name: myst
+    format_version: 0.12
+    jupytext_version: 1.9.1
+kernelspec:
+  display_name: Python 3
+  language: python
+  name: python3
+---
+
+```{currentmodule} tskit
+```
+
+(sec_analysing_tree_sequences)=
+
+# Analysing tree sequences
+
+:::{todo}
+Add all stats material from https://tskit.dev/tskit/docs/stable/tutorial.html
+
+Should we rename this "calculating statistics", or something else with the word "statistics" in the name?
+:::