I'm trying to replace the Git backend's use of Git notes for storing
metadata (#7). This patch adds a file format that I hope can be used
for that. It's a simple generic format for storing fixed-size keys and
associated variable-size values. The keys are stored in sorted
order. Each key is followed by an offset to the value. The offset is
relative to the first value. All values are concatenated after each
other. I suppose it's a bit like Git's pack files but lacking both
delta-encoding and compression.
Each file can also have a parent pointer (just like the index files
have), so we don't have to rewrite the whole file each time. As with
the index files, the new format squashes a file into its parent if it
contains more than half the number of entries of the parent. The code
is also based on `index.rs`.
Perhaps we can alo replace the default operation storage with this
format. Maybe also the native local backend's storage. We'll need
delta-encoding and compression soon then.
e86d266e6b