Derive rather than impl `Default` for `Fill` (#152) #549

Job	Run time
cargo check (msrv) (wasm32)	21s
cargo check (msrv) (windows-latest)	45s
cargo check (msrv) (macos-latest)	26s
cargo clippy (wasm32)	27s
cargo check (msrv) (ubuntu-latest)	19s
cargo clippy (windows-latest)	1m 2s
cargo clippy (macos-latest)	28s
cargo clippy (ubuntu-latest)	28s
cargo test (wasm32)	17s
formatting	28s
typos	4s
cargo test (ubuntu-latest)	22s
cargo test (macos-latest)	21s
cargo test (windows-latest)	46s
cargo doc	20s
	6m 54s

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