Adds merge_sort flag to unshard function.
Make things compile and fix a bug.
Made mock file support the use of semantic checking serializer.
Got things compiling in semantic serializer check + debug mode.
Adds a way to iterate a leaf node in reverse.
Change around gitignore files.
Made LBA hold and emit ser_block_size, but let that fact be mostly ignored.
Pushes the direction down further.

Everything compiles here.
Inspected uses of get_block_offset and put RSI comments on some of them.
Made us actually read the block size from entry.
Made old RSI comments about use-after-free bug be TODOs.
Made ls_block_token_pointee contain its int64_t offset.
Removed token_offsets map.
Added ser_block_size_ field to ls_block_token_pointee_t, but it always gets initialized with fake values.
Renamed gc_entry to gc_entry_t.  Finally.
Removed some whitespace.
Moved methods of gc_entry_t to top of class.
Renamed block_id in update_g_array to the more accurate block_index name.
Added all_garbage function, fixed other uses of block_id vs block_index.
Made garbage ratio be counted in terms of bytes, not blocks.