add afl tests for file reading and writing.

[emaxerrno]

I just added the american fuzzy lop to fuzz the inputs to the wal readers.

Need to fix the readers and writers of this stuff.

[emaxerrno]

https://github.com/google/honggfuzz/blob/master/docs/PersistentFuzzing.md

honggfuzz might be easier to integrate since it only requires a simple buffer size and pointer.

I dig. Could be very easy to integrate.

[emaxerrno]

https://github.com/chadaustin/sajson/blob/master/sajson-fuzz/run.sh use this example