B-tree & lfreq adjustments, slimSystem, add adix/amoft

Various B-tree fix-ups to make some things discardable/marked used/etc.

Allow user to boost util/lfreq data space, though it should be replaced by a less hokey thing when concepts work better..

Add new Count-Min Sketch-based adix/amoft.nim module for approximately k-most often problems, where right now k is not too large (probably need to tie into B-tree for large k and dynamically switch over for large k since the heap-scan-table is probably faster for k < 2000 which is likely the common case).