Tests

feat: add `abigen!` macro #989

Job	Run time
Unix tests (ubuntu-latest, stable)	4m 28s
Unix tests (ubuntu-latest, nightly)	2m 17s
Unix tests (macos-11, stable)	4m 15s
Unix tests (macos-11, nightly)	4m 31s
Windows tests (stable, x86_64-pc-windows-gnu)	7m 31s
Windows tests (stable, x86_64-pc-windows-msvc)	6m 15s
Windows tests (nightly, x86_64-pc-windows-gnu)	5m 26s
Windows tests (nightly, x86_64-pc-windows-msvc)	9m 41s
no-std build	2m 56s
WASM tests	4m 54s
	52m 14s

Provide feedback