0.11-wip

Copied from #89 

- [x] #85 Allow saving of empty values
- [x] #88 Fix leak of options attribute
- [x] #84 Upgrade LevelDB to 0.15.0
- [ ] Something related to #82 - need to document the forks in the README so when you go to their "homepage" you get information that's actually relevant to the forks
- [x] Remove `-Wno-unused-local-typedefs` from binding.gyp. This is just something I put in there for OCD purposes, the current V8 in master falls foul of this new gcc warning and they still haven't fixed it but we might just put up with it for now since it seems to cause problems on older gcc (CENTOS ARGH!)
- [ ] Adopt node-pre-gyp for binary distributables--minly a concern for Windows but will also be helpful for Mac I imagine; not so concerned about Linux and it's actually the most diverse and difficult target
- [x] Upgrade to NAN 0.9 (unreleased)
- [ ] Update forks