- `ProbeFunction` is now an interface for easier use
- `ProbeFunction`s can be auto-updated with specified update interval
- `StatefulProbes` changed into `ManualProbes` and implement `ProbeFunction` interface
- `ManualProbes` allows for marking probe as unhealthy with custom cause
- handlers now return JSON response with failed probes
- handler's response can be set to verbose via `Kubeprobes` option or via `?v` request param
BREAKING CHANGE: type definitions were replaced with more robust implementation.
