Add support for modifying the last invocation of a command #1088

Job	Run time
Rustfmt	12s
Clippy	49s
Test (MSRV)	1m 40s
Build docs	1m 27s
Test (stable)	2m 9s
Test (beta)	2m 0s
Test (nightly)	1m 53s
Test (macOS)	1m 36s
Test (Windows)	5m 13s
Test (no features)	1m 17s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 20s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 16s
	20m 52s

Provide feedback