Refactor output path flags

nss: use certutil from $PATH if found on macOS (FiloSottile#71)

Fixes FiloSottile#70

Thanks to @hostep for testing and fixing the patch.

linux: use unique per-CA names when installing certificates

Fixes FiloSottile#52
Closes FiloSottile#59

Force go stable to workaround travis-ci/gimme#157

Add note about iOS bug to README

Fix getCAROOT switch statement

Delete local Homebrew Formula now that it's in homebrew-core

See FiloSottile#32