Cleanup the "tests" folder

[sofian]

• Replace the "tests" folder with an "examples" folder
• Maybe remove and rename some of the examples so that they are compliant with the rest of the nomenclature (eg. b-tree should be renamed "bt" like the src/plugins/bt folder).
• Maybe also add a README file that lists all the examples (or add them to the main README.markdown)

[sofian]

Done: Replace the "tests" folder with an "examples" folder