Bring more of the Velato runtime, including Composition, Renderer. (#15) #32

Job	Run time
cargo clippy (wasm32)	37s
cargo check (msrv) (wasm32)	37s
cargo check (msrv) (windows-latest)	1m 21s
cargo clippy (windows-latest)	1m 4s
cargo doc	25s
cargo check (msrv) (macos-latest)	46s
cargo clippy (macos-latest)	52s
formatting	25s
cargo check (msrv) (ubuntu-latest)	32s
cargo clippy (ubuntu-latest)	36s
cargo test (windows-latest)	1m 19s
cargo test (wasm32)	36s
typos	5s
cargo test (macos-latest)	41s
cargo test (ubuntu-latest)	31s
	10m 27s

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