Adding some new features

[KayEss]

Hi,

We're using this fork of rocksdb and have some plans to make some features available to Erlang. Most importantly we want to be able to open read-only views into database and control the updates of their snapshots. We'll also want to be able to open databases in read-only mode. I'm just looking starting to plan this out from our side and probably the first thing I'll try to work out is what the new APIs might look like. Is this anything that you're interested in seeing a PR for? I notice that this fork isn't really pushing its changing to its upstream on gitlab.

Before doing this I'm seeing some compiler warnings that could be fixed up. I could submit those as a separate PR to start with. I would also like to refresh the vendored libraries. Personally I think git submodules are easier to maintain then having the libraries vendored in (and this is our standard practice). I guess it's less likely you'll be interested in that, but I'm asking anyway.

If you're not interested in taking any of these changes that's fine. We'll just maintain our own fork and I'll be more aggressive at changing things to match how we normally work.