Notably, solaris/amd64 and illumos/amd64 were added in go1.13. The
others were have been supported previously but were not build targets.
After go1.13, nacl/* will no longer be supported and plan9/* is still
considered experiemental. As a result they are omitted.
In this commit, we create a new `build/release` package which houses the
build instructions and scripts that we need to do deterministic builds
across Windows, Linux, and MacOS.
With this new system, it's now possible for all `lnd` developers, as
well as users to verify the posted build binaries. This wasn't possible
in prior release as only in Go 1.13 did deterministic builds becomes
easier/possible. See the new `README.md` for further details.
