Support Solaris, take two

The golang.org/x/sys/unix package has everything we need, even if
syscall doesn't.

In the future, the rest of the Unix-like input_*.go files can be
simplified by using golang.org/x/sys/unix instead of syscall. For now,
only make this change for Solaris.

Revert "Support Solaris"

This reverts commit ecd7f94.

Revert "Add "golang.org/x/sys" to go.mod for Solaris"

This reverts commit 0896c1d.

Add a function to turn off beeping

Initial "go modules" tag

There have been many releases since v1.0.0, but "go get" has not used
tags before now (go1.11 was released).

While there have been many additions to the API, it probably isn't worth
counting them to get the semver exactly correct. Therefore, v1.1.0 is
the version I'm choosing for the first useful tag.

Add README