Convert a few more markdown-include plugin usages to pymdown.snippets extension syntax instead

Author: tleonhardt

docs/examples/getting_started.md

@@ -19,9 +19,7 @@ click the **Copy** button in the top-right):
 !!! example "getting_started.py"
 
     ```py
-    {%
-        include "../../examples/getting_started.py"
-    %}
+    --8<-- "examples/getting_started.py"
     ```
 
 ## Basic Application

docs/features/initialization.md

@@ -5,9 +5,7 @@ Here is a basic example `cmd2` application which demonstrates many capabilities
 !!! example "examples/getting_started.py"
 
     ```py
-    {%
-        include "../../examples/getting_started.py"
-    %}
+    --8<-- "examples/getting_started.py"
     ```
 
 ## Cmd class initializer

docs/features/settings.md

@@ -105,9 +105,7 @@ Here's an example, from
 !!! example "examples/environment.py"
 
     ```py
-    {%
-      include "../../examples/environment.py"
-    %}
+    --8<-- "examples/environment.py"
     ```
 
 If you want to be notified when a setting changes (as we do above), then be sure to supply a method