* voxel BVH

* more work on voxel BVH

* last work on voxel BVH

* 2D voxel BVH implementation

* renamed logregion to logtile

* added support for weak references

* gc now performs compaction in-place

* fixed GC implementation

* improved deduplication

* logregion: more ascii art

* more docs for logregions

* more logregion arithmetic

* dedup implementation

* cosmetic source fixes

* fix typo

* content-agnostic garbage collector implementation

* prototype logsuffix tree

* more work on new module format

* more work on UVM, logregion

* UVM: added sweep & mark gc mechanism test