Add `dec!()` macro by example #1079

Job	Run time
Check file formatting and style	1m 14s
Check minimum rust version	2m 41s
Check documentation	56s
Dependency Tests (stable)	2m 45s
Fuzz Tests	1m 6s
Dependency Tests (beta)	2m 42s
Database Tests - MySQL (stable)	1m 19s
Database Tests - PostgreSQL (stable)	3m 0s
Database Tests - MySQL (beta)	1m 19s
Database Tests - PostgreSQL (beta)	2m 56s
Standard Tests (stable)	2m 24s
Standard Tests (beta)	2m 28s
Database Tests	1s
Test	1s
Pass	1s
	24m 53s

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