enhance documentation

- flatten hierarchy (some links do not work when using folders)
- add a tutorial for programming a simple driver
- clean description using inspect.cleandoc
+ fix a bug with 'unit' pseudo property in a Parameter used as override

Change-Id: I31ddba5d516d1ee5e785e28fbd79fca44ed23f5e
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/25000
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

doc/source/secop_demo.rst

@@ -0,0 +1,10 @@
+Demo
+====
+
+.. automodule:: secop_demo.cryo
+    :show-inheritance:
+    :members:
+
+.. automodule:: secop_demo.test
+    :show-inheritance:
+    :members: