variable length blocks, typing, TreeMap

Well, I've now defined a simple root block (with no content) and the logic for determining its location and where to write it to next. I've also finished the physical layer of the database.

I'll note that the root block is the only block with a maximum size (default is 8K). Everything else is variable in size, and that is a big advantage to a copy-on-write database--handling variable length blocks is easy! Of course, this means we can easily use compression on the data. :-)

It is time to add support for multiple logical block types by having a type string as the first data element for all logical blocks.

It is also time to define a logical block type which holds data. TreeMap is my prefered choice. Root can then subclass the TreeMap logical block.