Large object storage (#125)
vsql now supports storing objects (rows, tables, etc) larger than a page
(which previously was a serious limitation). This happens entirely
transparently on the B-tree implementation where larger objects are
split (and reconstructed) to and from new `B` (blob) and `F` (fragment)
objects.
This is a breaking change to the file format. Some other notable
improvements:
- Documentation now has Excalidraw diagrams. The "File Format" page has
been totally overhauled and is a lot easier to understand and much
nicer to look at: https://vsql.readthedocs.io/en/latest/file-format.html
- Added "Limitations" page. Among which, a vsql file - in theory - can
hold up to 128PB (wholly untested, of course).
- Page splitting now has a heavy bias towards filling the left page as
much as possible (rather than even splitting). We prefer the left page
to be a full as possible because the keys are sequential, so in the case
of lots of sequential inserts it can pack the data more tightly and
causes less page splits as new data is inserted.
- Added another B-tree test for testing 100k sequential inserts/deletes
and improved the existing random insert/remove test matrix from just 48
byte objects to also include 148 byte objects (one object per page) and
348 byte objects (always using blob storage).
Fixes #43
