Fix comment typo.
Track execve.

Closes #1.
fingerprint: Use a standard flexible type.

It turns out we don't actually need to care about the width of this type,
because we don't really need to know its on-disk representation.
Improve 'operation' schema.

The previous table schema had a little fragility in that collisions could
happen when processes had equivalent concatenated arguments. E.g. the command
`cp "foo bar" baz` would be considered equivalent to `cp foo "bar baz"`. The
new table schema encodes the argument character lengths, which should prevent
these situations.
s/operation/trace.