Some fields were introduced to Chart metadata after Alpha.4, but are not
going to be used ever. So we made the decision to remove them before we
get stuck with ugliness.
This should not break compatibility, since these fields were not used.
This is a refactor of the loader to use in-memory buffers instead of
trying to optimize for memory usage by delaying reads until the last
possible moment. Since charts tend to stay well below 1M in size, this
makes more sense, and is easier to work with.