Update ERC20 to match specification (#231)

* Update ERC20 to match specification

Some names and functions don't match specification.

https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md

* Cargo fmt
10 jobs for master in 2 minutes and 52 seconds (queued for 15 minutes and 34 seconds)
Status Job ID Name Coverage
  Check Workspace
failed #271205
linux-docker
cargo-build-nf

00:00:44

failed #271199
linux-docker
cargo-check-af

00:01:20

failed #271200
linux-docker
cargo-check-nf

00:01:10

failed #271202
linux-docker
cargo-clippy-af

00:00:44

failed #271203
linux-docker
cargo-clippy-nf

00:00:43

failed #271201
linux-docker
cargo-fmt

00:01:00

failed #271204
linux-docker
cargo-test-af

00:00:41

 
  Examples
skipped #271208
linux-docker
examples-abi
skipped #271207
linux-docker
examples-test
skipped #271206
linux-docker
examples-wasm
 
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cargo-build-nf Check Workspace
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cargo-test-af Check Workspace
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cargo-clippy-nf Check Workspace
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cargo-fmt Check Workspace
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cargo-clippy-af Check Workspace
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cargo-check-nf Check Workspace
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cargo-check-af Check Workspace
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