Merge branch 'update'
* new custom variables db_name and collection_name
* degraded db and collection from params to options (with custom vars as default values) in poly_db, poly_db_one and poly_db_count
* removed smooth_reflexive wrapper function since one can now set the custom variable instead
* some polishing of the code
* adapted DatabaseCursor to the new custom variables
* improved documentation (link to tutorial)
Merge branch 'master' into update