Issue #16827: Make Interpreter introduction section of the tutorial more
focussed and move advanced section and customization information to a separate
file called appendix.

Patch credits: Jamayla Wiley, Ya-Ting Huang and James Brewer.

--HG--
branch : 2.7
Issue #22436: Improved documentation for getEffectiveLevel() and getLevelName().

--HG--
branch : 2.7