move the bookmark to a new namespace 'Editor'
change header of Chunk_Manager.foreach_model function
add parameter z to Chunk_Manager.Chunk.drop
add Chunk_Manager.Chunk.update() and fixup for its init()
add collision functions in Chunk_Manager
fixup Entity class (data types, paramters to .draw function, ...)
add Error_Manager.last_error
add Instance.aborted
fixup doc and datatypes in Model class
fixup datatypes in Option_Manager class
refactor Player.Control
fixup player (no more "using ...", ...)
fixup Database_Sqlite class (memory mgmt)
split the player class into one abstract class and one in namespace Jumpfree.Jump
add Entity_Physics class in namespace Jumpfree.Jump