Add IsWriterTerminal and IsWriterCygwinTerminal functions (fixes #80)

chore: updates post-fork repo

Update golang.org/x/sys dependency

tests: log value of IsTerminal

Add mailmap to fix authorship inconsitencies

CI: add Go 1.20

deps: use a tagged version of golang.org/x/sys

Check for `io.Writer`

Adjust build tags to allow building on tinygo; for #73.

Update golang.org/x/sys commit hash to 0f9fa26a