doc: Adding part 1 of the getting started tutorial

  o doc/Makefile: Added new directory to collect rst files from

  o doc/examples/first-project: Added the "first-project" example
    project.

  o doc/source/sessions/first-project-*.html: Added the generated
    snippets

  o doc/source/using_tutorial.rst: Added the new main tutorial page

  o doc/source/tutorial/first-project.rst: Added part 1 of the tutorial here

  o tests/examples/first-project.py: Added test for the example project

This is largely based on an example by Javier Jardón, which was
submitted at !323

Fixes #103