v1.27.0: allow redirection to /dev/stderr on Windows, more

What's changed

• Fix wrong precedence of 'expr | getline' expressions by @fioriandrea in #216
• Use C.UTF-8 as locale when invoking external awk program by @guilherme-puida in #226 (first-time contributor)
• New feature: Make redirecting to /dev/stderr work on Windows by @benhoyt in #225

Full Changelog: v1.26.0...v1.27.0