improve API documentation

## Trac Ticket #38
**component:** documentation
**owner:** martin
**reporter:** martin
**created:** 2014-03-19 20:40:36
**milestone:** 
**type:** task
**version:** 
**keywords:** 

in wiki:API

## comment 1
**time:** 2015-12-11 15:28:51
**author:** martinP


also document the Delta format in /BivesDelta
