v0.6.0

• Update to serde 0.9
• Use serde_derive instead of manual codegen
• Enable most features by default. This increases compile times a bit, but is way less confusing for people since components aren't randomly missing.
• Drop TOML support. The toml crate hasn't yet been released with support for serde 0.9, but we'll add support back when that lands.
• Restructure config deserialization. A log4rs config can now be embedded in other config structures and deserialized by downstream users.