Update documentation structure and start migrating to markdown (#934)

Starts structuring the documentation library usage into Tutorials, Guides, Explanations and Reference.
Continues migrating new docs from rst to markdown.
Extends the test framework discovery mocks to allow easy writing and testing of code examples.

docs/source/tutorial.md

@@ -1,4 +1,4 @@
-# Tutorial
+# Getting started
 
 ```{eval-rst}
 .. automodule:: tutorial