Log Message:
Add a package for Go 1.15.

The latest Go release, version 1.15, arrives six months after Go 1.14. Most of
its changes are in the implementation of the toolchain, runtime, and libraries.
As always, the release maintains the Go 1 promise of compatibility. We expect
almost all Go programs to continue to compile and run as before.

Go 1.15 includes substantial improvements to the linker, improves allocation
for small objects at high core counts, and deprecates X.509 CommonName. GOPROXY
now supports skipping proxies that return errors and a new embedded tzdata
package has been added.

There are no changes to the language.