Packages in Go serve the same purposes as libraries or modules
in other languages, supporting modularity, encapsulation, separate compilation,
and reuse. The source code for a package resides in one or more
.go files, usually in a directory whose name ends with the
import path; for instance, the files of the
gopl.io/ch1/helloworld package are
stored in directory
Each package serves as a separate name space for its declarations.
image package, for example, the identifier
Decode refers to a different function than does the same identifier
To refer to a function from
outside its package, we must qualify the identifier to make explicit whether ...