feat: Add support for Key-Value data in log records.

See rust-lang/log#328

Author: tmccombs

Cargo.lock

@@ -42,6 +42,7 @@ color = ["dep:termcolor"]
 auto-color = ["dep:is-terminal", "color"]
 humantime = ["dep:humantime"]
 regex = ["dep:regex"]
+kv_unstable = ["log/kv_unstable"]
 
 [dependencies]
 log = { version = "0.4.8", features = ["std"] }