Corrections for 2.0

* modified pricing
* added categories
* added code samples
* added fenced code block "ninja"

Signed-off-by: Jérôme Coupé <jercoupe@gmail.com>
Merge branch 'master' of github.com:jeromecoupe/iad_craftcms_introduction

Signed-off-by: Jérôme Coupé <jercoupe@gmail.com>

Conflicts:
	craft_introduction.md