implement a basic test for Block::put, ::top and ::take
doc
move creation of block for tests to helper method for more flexibility
rename  method
add method to manipulate status of Item (for whitebox testing)
allow to mark items dead on creation
handle dead or taken elements during partitioning
test partition with block that contains only dead items
ref
check if left points to dead item when partition finsished
doc
don't add a partition pointer for empty partition
provide basic reference counting for PivotElements
use reference counting for PivotElements
using ctest to be able to run all tests from command line
increment refcnt for PivotElement on put
return correct max partition size
iterate through all items in partition more cleanly
fall back to previous partition only if possible
doc