rework permission checks #34

Job	Run time
Rustfmt	12s
Clippy	49s
Build docs	1m 21s
Test (MSRV)	1m 21s
Test (stable)	1m 57s
Test (beta)	2m 2s
Test (nightly)	1m 43s
Test (macOS)	1m 35s
Test (Windows)	3m 58s
Test (no features)	1m 15s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 13s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 23s
	18m 49s

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