v4.0.0-release

• conceal set now supports secret values being set from STDIN
• conceal update added to allow updating secrets in place, supports STDIN
• conceal summon install added to implement a conceal_summon provider for Summon
• conceal summon show added to support the conceal_summon provider's requirement for the secret value to be returned to STDOUT for Summon to act upon
• Added tests for keychain.go and clipboard.go packages
• Added stylized responses from CLI in Terminal