Update test matrix to go1.22, go1.21, and go1.20

Merge pull request #99 from go-cmd/dn/v1.4.2

Prepare v1.4.2: update docs, go.mod, some code comments

Add v1.4.1 to CHANGELOG

Merge pull request #75 from go-cmd/dn/v1.4

Rework Cmd.Options as Options.BeforeExec

Update changelog for v1.3.1

Merge pull request #52 from go-cmd/dn/fix-stop-issue-16

Add ErrNotStarted and return from Stop() (fixes #16)

v1.2.1: Fix/add godoc. Remove go1.12, add 1.14 to travis. Update godep.

Merge pull request #43 from go-cmd/close-streaming-chans

Close streaming output channels

Merge pull request #39 from go-cmd/windows-process-kill

Test on Windows

Merge pull request #37 from akkumar/gomod

Gomod