Hi,
Sorry, but there is not developement manual.

Best way is : get into the code and understand how it's done (not so complicated

).
Steps to add new object are :
- Create new table objectclass
- Add a line in table menu for the new object
- Add lines in habilitation table
- If object is project dependent, add lines in accessrights table
- Add new objectClass.php, including fields in table objectclass
- Define new iconclass for class projectorIcon.css, and include corresponding images
- Include new texts in lang.xls and generate new lang.js file
Best is to start from existing one : select one item looking like your new class, and copy as new objectClass.php
You'll find database instructions exemples in /db/vx.y.z.sql files : start by copying instructions concerning the copied item...
If you get something intereting, maybe you can share it to the community
Have good work !
Babynus.