Instead of writing each byte alone to the console, always write the
full plain text up to the next escape sequence or until the write
is finished.
Doing so means more copying around of bytes, but improves write
performance significantly.

Starting with Go 1.17, //go:build lines are preferred over // +build
lines, see https://golang.org/doc/go1.17#build-lines and
https://golang.org/design/draft-gobuild for details.

This change was generated by running Go 1.17 `go fmt ./...` which
automatically adds //go:build lines based on the existing // +build
lines.

Add //go:build lines

Write plain text in chunks

Travis CI no longer seems to be working:
https://app.travis-ci.com/github/mattn/go-colorable

Add a GitHub action instead, based on the one from
github.com/mattn/go-isatty

Migrate to GitHub actions for CI testing

There is a typo in the actions/setup-go step which leads to the Go
version not being picked up correctly. Fix it.

Use correct field to specify Go version in GitHub action

buf(bytes.Buffer) is actually unused.

delete buf