testing pull request on reforked repo

- shorten the code of replaceByClumps() in yadeWrapper.cpp

- check number of clump members in releaseFromClump() method, body will be not released if number  of clump members = 2, a warning will occur in this case

- check length of python input in replaceByClumps() method

- check if amount < 0 in replaceByClumps() method

- some improvements and fixes in documentation