When `helm install -f foo.yaml bar` is called, and then the release is
upgraded with `helm upgrade happy-panda bar`, this will now re-use the
values that were submitted with `-f foo.yaml`. The same is true for
values specified with `--set`.
Closes#1227
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.
