Various improvements to `zlog` including:
- Enable filtering by module (reproducing `env_logger` behavior) both
through env and settings.
- Note: filtering by module currently does not account for parent module
configuration, but does account for crate configuration.
i.e. `crate=trace` will enable `TRACE` messages in `crate::a` and
`crate::a::b` modules, but `crate::a=trace` will not enable trace
messages in module `crate::a::b`
- Implementing the `Log` trait for `zlog::Logger` to support gradual
transition and evaluate tradeoffs of always going through `log` crate.
- Added the ability to turn off logging for a specific filter (module or
scope) completely by setting it to `off` (in env: `crate::a=off`, in
settings: `"project.foo": "off"`)
- Made it so the `zlog::scoped!` macro can be used in constant
expressions, so scoped loggers can be declared as global constants
Release Notes:
- N/A
Ben Kunkle
