This reorganizes the developer's main page by adding a
'Commands and API References' section at the same level
as the sections for Administrator's & Developer's guides.
It also removes subsections like 'Introduction' and 'Overview'
that didn't make sense any more since they included more than
one might expect from such sections.
Change-Id: Ibf5415d946238ffadedc36c9a731f773f4fa2d71
2ef3b403e4