feat(encoding): encode usize and isize #1020

Job	Run time
Clippy	1m 14s
Check rustdoc intra-doc links	33s
Cross compile (armv7-unknown-linux-gnueabihf)	20s
Cross compile (powerpc-unknown-linux-gnu)	20s
Cross compile (powerpc64-unknown-linux-gnu)	23s
Rustfmt	19s
Check	1m 34s
Test Suite	1m 53s
Cross compile (wasm32-unknown-unknown)	19s
	6m 55s

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