libraries for advanced Go linter

 Libraries to implement following tools:
  * keyify: Transforms an unkeyed struct literal into a keyed one.
  * rdeps: Find all reverse dependencies of a set of packages.
  * staticcheck: Go static analysis, detecting bugs, performance issues, and
    much more.
  * structlayout: Displays the layout (field sizes and padding) of structs.
  * structlayout-optimize: Reorders struct fields to minimize the amount of
    padding.
  * structlayout-pretty: Formats the output of structlayout with ASCII art.