Fix missing or unspecific dependencies.

- levelup v0.19.0 requires leveldown 0.10.0 (apparently)
- semaphore and jayson packages missing from package.json

[d11e9]
Merge pull request #1 from d11e9/master

Fix missing or unspecific dependencies.
Merge pull request #9 from projectdnet/master

Fix missing or unspecific dependencies.