Move all documentation to 'doc' directory

Remove clutter from top level directory

Change-Id: I458e424148762b0b8131743fce97f326fe6439fe
Reviewed-on: http://review.couchbase.org/43689
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>