Add new --style called header-filesize and display it by default (#1988)

Also rename `header` to `header-filename`.

Related to #1701

Cargo.toml

@@ -65,6 +65,7 @@ dirs-next = { version = "2.0.0", optional = true }
 grep-cli = { version = "0.1.6", optional = true }
 regex = { version = "1.0", optional = true }
 walkdir = { version = "2.0", optional = true }
+bytesize = { version = "1.1.0" }
 
 [dependencies.git2]
 version = "0.13"