## Motivation
As discussed in #308, there are a large number of crates in this
repository, which can be confusing for users and can increase the
maintainance burden for maintainers. Also, the `tracing-fmt` and
`tracing-subscriber` crates both contain filtering implementations with
similar behaviour and APIs, but `tracing-subscriber`'s filter module
offers more advanced features (filtering on field values), and is usable
with any subscriber implementation. Two separate filter implementations
also has the potential to be confusing for users.
## Solution
This branch moves most of the code from `tracing-fmt` into a module in
`tracing-subscriber`, and changes the `tracing-fmt` builder APIs to use
the `Filter` type in `tracing-subscriber`. The `tracing-subscriber/fmt`
feature flag can be used to disable the formatting subscriber when it is
not used.
The `tracing-fmt` crate has been updated to re-export the APIs from
`tracing-subscriber`, and marked as deprecated. Once we've published a
new version of `tracing-subscriber` with the format APIs, we can publish
a final release of `tracing-fmt` that will update the documentation &
mark all APIs as deprecated, so that users know to move to the
`tracing-subscriber` crate.
Refs: #308
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
