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