Adds references and branches slides

Mostly adds slides about references and branches. Also tweaked python
start code and re-aranged / tweaked some existing slides

shell/branch-diff

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+cd /tmp/demo/
+
+echo '$ git log --oneline --all --graph'
+git -c color.ui=always log --oneline --all --graph --decorate=short
+
+echo '$ git diff mater..test'
+git -c color.ui=always diff master..test

shell/cat-master-and-head

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+cd /tmp/demo
+
+echo '$ cat .git/refs/heads/master'
+cat .git/refs/heads/master
+echo '$ cat .git/HEAD'
+cat .git/HEAD

shell/create-first-branch

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+
+cd /tmp/demo
+git switch master > /dev/null
+git branch -D test > /dev/null
+echo '$ git branch -v'
+git -c color.ui=always branch -v
+echo '$ git switch -c test'
+git -c color.ui=always switch -c test
+echo '$ git branch -v'
+git -c color.ui=always branch -v
+echo '$ git log --oneline --all'
+git -c color.ui=always log --oneline --all --decorate=short

shell/delete-test-branch

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+cd /tmp/demo
+echo '$ git switch master'
+git switch master
+echo '$ git branch -d test'
+git branch -d test

shell/differing-branches-simple

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+cd /tmp/demo
+echo '$ git switch master'
+git switch master
+echo '$ vim greeting.py'
+sed -i 's/Hello World/HELLO WORLD/g' greeting.py > /dev/null
+echo '  # CAPITALISE HELLO WORLD #'
+echo '$ git commit -am "Capitalises Hello World"'
+git -c color.ui=always commit -am "Capitalises Hello World"
+echo '$ git switch test'
+git switch test
+echo '$ vim greeting.py'
+sed -i '3iimport sys\n' greeting.py > /dev/null
+echo '  # Adds the line "import sys" #'
+echo '$ git commit -am "Adds sys import for arg parsing"'
+git commit -am "Adds sys import for arg parsing"
+#echo '$ git diff master..test'
+#git -c color.ui=always diff master..test
+#echo '$ git log --all --oneline --graph'
+#git -c color.ui=always log --all --oneline --graph --decorate=short

shell/git-init

@@ -6,3 +6,5 @@ echo '$ cd /tmp/demo'
 cd /tmp/demo/
 echo '$ git init'
 git -c colour.ui=always init
+echo '$ git status'
+git -c colour.ui=always status

shell/simple-merge

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+cd /tmp/demo
+echo '$ git switch master'
+git switch master
+echo '$ git merge test'
+git merge test
+echo '$ git log --oneline --all --graph'
+git -c color.ui=always log --oneline --all --graph --decorate=short